IESpell is a free Internet Explorer browser extension that spell-checks text-input boxes on a Web page. It should come in particularly handy for users who do a lot of Web-based text entry (Web mail, forums, blogs, diaries). Even if your Web application already includes spell-checking functionality, this utility is faster than a server-side solution. Plus, you get to store and use your personal word list across all your applications instead of having to maintain separate ones on each application.
What's new in this version:
Version 2.6.4 build 573 fixes an issue with spell checking large documents (>30k characters) with lots of custom tags (e.g. Wikipedia pages). The text parsing code was rewritten to make it more robust and alot quicker too.