there is this web based app:
http://www.apple.com/webapps/productivity/mobilewebdocs_johnswanson.html
I believe that the touch can open excel files from attachments in an email I think, not sure about other types maybe powerpoint documents aswell.
also found something called
readdle, theres a review here:
http://itouchtips.wordpress.com/2007/12/18/ipod-touch-document-viewers/. The plans for this app are
free account:
Documents/books per account: 20
Storage amount: 50MB
doc, fb2, gif, html, jpeg, pdf, rtf, txt, xls and pdb(Plucker) file support
Text appearance settings
$5 account:
Documents/books per account: 500
Storage amount: 1GB
doc, fb2, gif, html, jpeg, pdf, rtf, txt, xls and pdb(Plucker) file support
Offline access to documents (file size limit is 100kB)
Uploading documents by e-mail
Text appearance settings
Page bookmarks
15-day trial
Priority support
$10 account:
Documents/books per account: Unlimited
Storage amount: 5GB
doc, fb2, gif, html, jpeg, pdf, rtf, txt, xls and pdb(Plucker) file support
Offline access to documents (file size limit is 100kB)
Uploading documents by e-mail
Text appearance settings
Page bookmarks
15-day trial
Priority support