ieSpell - A Spell Check Addon for Internet Explorer 7
Unfortunately the Microsoft team did not think that a spell checker was an essential tool for the browser, Firefox on the other hand have a build-in Spell checker but Internet Explroere does not, so to add that functionality you can install an addon for ieSpell checker.

Add-Ons Source : Download ieSpell

InLine Search  - Search the page for words or paragraphs
While searching around the internet you come up to a page and find out that the keyword you used to find the page is not clearly visible on the page. To do so you can use the find in page facility in IE7 [ctr +F5] but the search facility is not that great. Inline Search is an add-on for Internet Explorer that mimics Firefox’s search behavior, it turns searching into a Web page into a non modal research experience coupled with a search as you type facility.

Add-Ons Source : Download InLine Search for IE7

Download Video’s Via Internet Explorer 7 Add Ons
Download videos from Youtube, Google Video, Grinvi, and many other sites with simply one click. This simple add-on adds a Download Video link to the right click menu panel. Just click on it and a new window will be displayed with the download link. You will be able to download videos to your computer and watch them as many times as you want.

Add-Ons Source : Video Download for IE7

YouTube Video Download
Another add ons to download flv videos from youTube using  “YouTube Grabber for IE7″, simply past the URL of the video into the addons and press Grab and you can download the vide.

Add-Ons Source : YouTube Grabber for IE7

Internet Download Accelerator  Add Ons
Internet Download Accelerator lets you conveniently manage downloads by organizing them in categories with automatic category detection option. The option to listen to/view audio/video files as early as download starts will let you filter out unwanted content immediately.Another feature is the original Active Visual Cart technology which significantly improves your download experience by giving you quick access to the most useful program features without opening the main program window.

Add-Ons Source : Internet Download Accelerator for IE7