ieSpell

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.