If you're not using the firefox browser yet, you should be. It's a free web browser that you can use instead of Microsoft's Internet Explorer. It's an open source application, meaning it was created by a bunch of programmers that came together to make the world a better place, and don't make a penny off of it. It doesn't have all of the holes that Internet Explorer has and it has a ton of great extensions that can be added to it to customize and add functionality.
Here are the extensions I've added in so far.

• Clone Window - Let's you duplicate the window or tab that you're currently viewing, complete with content and browse history.
• Spellbound - Adds spell check functionality to your text.
• A9 Toolbar - Provides A9 search capability in the browser
• ForecastFox - Inline weather forecast, giving a three day forecast in the bottom of your browser toolbar.
• Yahoo Companion - Integrates in with my e-mail and yahoo portal functionality
• Bloglines - Let's me easily add blogs into my bloglines.com RSS reader account.
• Stock Ticker - Shows my stocks in a ticker at the bottom of my browser window.

You can find a million more at this firefox extensions site.