Safari (possibly all of the browsers on a Mac since spell check is a core service) will allow you to spell check any text field by pressing cmd ;. Pretty handy, I am sure there has to be a spell check plug-in for most browsers. Are web based spell checkers really any good? I have used the gmail one and it is good in a pinch, but I recall being annoyed by the other ones I have tried (yahoo and hotmail are the only ones I can recall).