I don't know that there are any with spell/grammar check but having used QuickOffice Pro HD, Kingsoft Office, and OfficeSuite Pro 6 (all of which are on my Prime right now), I can't give a high enough recommendation to OfficeSuite Pro 6. It's head and shoulders above the rest of the office programs out there.
Kingsoft Office is 100% free, and well worth it to have; it suffers largely from not being able to search for text or jump to pages, and I don't think it handles bullets and lists and such very well; however, for a free office app it's pretty full-featured.
OfficeSuite Pro just keeps getting better and better with each release, and I expect it won't be long before they add spell and grammar check, and the ability to create headers and footers (it supports headers and footers in pre-existing docs now). It's $15 or $20, I think, but well worth the purchase price.
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