I've used DocsToGo, which syncs with both Dropbox and Google Docs.
<a href="http://www.dataviz.com/products/documentstogo/" rel="nofollow">http://www.dataviz.com/products/documentstogo/</a><p>I've also used PlainText, which is without question the best text editing tool on the iphone and ipad. The dropbox integration is sick.
<a href="http://www.hogbaysoftware.com/products/plaintext" rel="nofollow">http://www.hogbaysoftware.com/products/plaintext</a>