These days we have great choices for Web browsers: Internet Explorer, Firefox, Safari, Opera, Chrome and the list goes on.

Each browser comes with its own set of advantages and features and one of the greatest benefits of Firefox has been the ability to fully customize it through the use of plugins and add-ons.

This feature is especially important for those of you using Mac OS X, when deciding whether to pick one of the two heavyweights: Firefox or Safari.

But Safari actually does support plugins. While the choice is nowhere near as extensive as that of Firefox, there is still a good variety of them to choose from.

Here's a list of 20 useful plugins for Safari for OS X.

Please note that many plugins work through something called SIMBL (Simple InputManager Bundle Loader), which is basically a little tool that helps developers manage and run their code as plugins for the different applications on OS X.

You can grab SIMBL for free here. If any of the following need SIMBL to run, just install SIMBL and drop the plugin file into your "~/Library/Application Support/SIMBL/Plugins/" folder, though be sure to read the instructions that come with each plugin as well.

1. Xmarks

Firefox had a very popular plugin called Foxmarks. This plugin still exists but the name has changed to Xmarks, and with the name change also came the support for other browsers, namely Internet Explorer and Safari.

Xmarks provides a seamless solution for syncing your bookmarks across many computers, as well as the ability to view your bookmarks online.

If you use several computers and want to have the same set of bookmarks across all of them without any fuss, Xmarks is the solution for you. Plugin website

2. Pith Helmet

PithHelmet is a blocker, but it blocks more than just ads. PithHelmet allows you to block things like Flash movies, Shockwave apps and those annoying midi sound loops.

Customize the filter however you like. Currently doesn't support Safari 4 beta. Plugin website

3. DeliciousSafari

del.icio.us is a bookmarking service that lets you store and share all your bookmarks in one place on the web.

You can also tag your bookmarks allowing for better methods of browsing through them. The DeliciousSafari plugin fully integrates with the service, allowing you to bookmark all your favorite sites without having to go to the site itself. Plugin website

4. Safari Tidy

This is a great plugin to help you validate your code. When running, it adds a little icon in the status bar together with the total number of warnings or errors that the current page has.

If you view page source using Safari, you'll see any lines that were mentioned in the warnings and errors highlighted, and you'll also see a summary of them at the bottom of the source view. Plugin website

5. SafariSource

The default Safari page source view leaves a lot to be desired. This simple plugin adds syntax coloring, which makes scanning source code a lot easier.

You can customize colors and fonts in the preferences pane that the plugin adds to the Safari preferences window. Plugin website

6. SafariStand

SafariStand is a useful little plugin that adds a thumbnail sidebar and a bookmarks shelf.

The shelf lets you easily save your browsing sessions and then resume them at the click of a button.

Other features include site alteration (e.g. modify the minimum font size on a particular site, use a custom style sheet or a different user agent) and an Action Menu, which allows you to easily browse the various assets that a site has, such as Javascript, CSS and cookies. Plugin website

7. Saft

Saft is like a Swiss Army Knife. It does so many things that it would take too long to list them all here. Here's a link to the full list of features.

Some notable ones include: ad blocking, always open new windows in tabs, block animations, undo support for closing tabs, sidebar, Growl support, Kiosk mode and full screen browsing. Plugin website

8. Cooliris

Cooliris is a great plugin for viewing image and video galleries, such as those on Google image search, Facebook, YouTube or Flickr.

At the click of a button the gallery on a web page turns into a full screen view where you can see all the photos and videos as well as zoom and pan around using the Cooliris interface.

It features a beautiful interface with smooth animations and transitions that delivers a very satisfying browsing experience. Plugin website

9. Inquisitor

Inquisitor is a great plugin to enhance the Google search field.

It runs the search live as you type it and brings in the results in a little window that pops up below the search. It can list results and search suggestions and you can customize how many of each you want to see.

It's a very high quality plugin, so much so that Yahoo has recently purchased it and is working on versions for Internet Explorer and Firefox.

Note: the Yahoo purchase also means that the search engine powering Inquisitor has now been changed from Google to Yahoo, so this is something to consider before you install the plugin. Plugin website

10. Safari140

Find something interesting on the Web that you just have to share on Twitter? The Safari140 plugin makes this easy.

It allows you to write Twitter messages from an integrated menu in Safari, and will even pre-fill and shorten the URL address of the current site you're browsing. Plugin website

11. 1Password

1Password isn't just a plugin, it's a whole password management service that comes with browser integration.

The benefit of using 1Password is that you can automatically generally really strong passwords and the service will then remember and automatically fill them in for you. The service costs $39.95, but there is a free trial available. Plugin website

12. TabExposé

OS X comes with a great method for managing windows on your desktop called Exposé, which at the click of a button shows you an overview of all of your open windows.

The TabExposé plugin works the same way, but for opening tabs in Safari. Plugin website

13. GreaseKit

Power users of Firefox utilize a plugin called Greasemonkey to modify any website they browse using bits of JavaScript.

This really enhances your browsing experience as you can, for example, modify the font sizes and colors on your favorite sites to make them more readable.

GreaseKit aims to fulfill this need for Safari, as well as other WebKit applications on OS X. Plugin website

14. SafariStretch

One of the key differences between window management in OS X and Windows is the maximize button.

In Windows, the maximize button makes the window full screen, and in OS X, the window becomes only as large as its content.

SafariStretch allows you to have the Windows-like full screen maximize in Safari. Plugin website

15. Glims

Glims is a plugin which adds a whole collection of features and functionality to Safari and aims to be the alternative to Saft.

The full list of features can be found on the Glims website, but some notable ones include: thumbnails in Google and Yahoo search results, full-screen browsing, favicons in tab labels, auto-close download window, always open links in new tab, close tabs using middle mouse button and dated download folders. Plugin website

16. CosmoPod

CosmoPod lets you download and convert Flash, DivX, WMV and Real Media videos from the Web to your Mac, iPod/iPhone or AppleTV. CosmoPod works with most sites and will automatically detect any videos it can convert.

With just a click you can then download the video to your iTunes library. Full license costs $10. Plugin website

17. CutX

CutX is a plugin that lets you create a filter for sites that you want to block.

This is useful as a parental tool to ensure your children don't visit the wrong sites, or for filtering those productivity drains from the workplace.

CutX lets you customize site filters for individual users and access to the preferences pane is protected by a master password. Plugin website

18. DownloadComment

DownloadComment is a simple plugin that makes use of the Spotlight comments section in the file properties on OS X.

Whenever you download a file, DownloadComment will attach the URL address of the file into this comments section allowing you to later see where a file has been downloaded from. Plugin website

19. Safarilicious

An alternative to the DeliciousSafari plugin, Safarilicious is a standalone app that will export your Safari bookmarks to del.icio.us, a popular bookmarking service.

Safarilicious can also generate del.icio.us tags from your bookmarks folder structure as well as letting you add your own.

You can also pick which folders get exported if you only want to share a certain set of bookmarks. Plugin website

20. Safari Microformats

Microformats are a set of data formats that aim to make information sharing easier across the Web.

For example, hCards and hCalendars contain contact and calendar information respectively and are formatted in a consistent way to allow different applications to read this data.

The Safari Microformats plugin reads any hCards or hCalendars present on a web page and notifies you with a little icon in the address bar.

When you click this Microformats icon you can add these addresses or calendar items to your Address Book and iCal. Plugin website

Written exclusively for WDD by Dmitry Fadeyev. He runs a blog on usability called Usability Post.

Do you know of any more useful Safari plugins? Please share them by leaving a comment below...