Weaver
Sage
I've used it a few times, and it is pretty useful, though it does have its faults. More than once it's asked me if I want to replace "sighed" with "side", which makes absolutely no sense.
Funniest true story I've ever heard about weird spell-check "corrections": A university professor I knew said that his spell check always told him to replace his own last name (Mesa-Guido) with "misguided."