yep, openoffice files are a good standard to use since the openoffice program is free for everybody to use, is *properly* cross platform (unlike txt, doc etc programs) and people who come here are quite likely to have it installed on their computer already.
either that or the (admittedly closed) pdf format would be good too, since the documents tend to look the same across platforms and readers, and you can make pdfs just as easily with openoffice.org too.