abiword?
OpenOffice.org?
I don't know if they are better then word is in terms of spell checking, but you can try them out, they are free.
OpenOffice.org is a attempt at creating a open source alternative to MS Office. It's free, it user interface is designed to be familar to MS Office users and it incorporates a full office production suite: Spreadsheet, word proccessing, powerpoint-style presentation, etc etc.
Office can be a bit of a pain because you have to install seperate
dictionaries and stuff based on your language, or something like that. But I think that it's worth the extra effort to get a big dictionary aviable to you for spell checking and looking up stuff.
Abiword on the otherhand is a small executable, very fast, and is designed just for Word proccessing. It's not a entire bunch of programs like O

rg and is pretty slick.
Both are free (no-cost and open source) software.