I'm accessing my Calibre ebook library (2 books as I experiment) on my ipod Touch's Stanza via a hand generated XML file. I've asked Kovid to add a feature to get Calibre to generate this for us as most of the info is already in Calibre's DB. The post hasn't been approved yet as it contains a screenshot from my touch.
With the XML atom feed you can see the cover image in Stanza's library screen and the Calibre converted epub's view great in Stanza with the correct cover, TOC and meta info. I just went to Settings->Stanza->advanced and changed the catalog url to http://myserver/ebooks/stanza.xml
and made sure the XML file was in this location. Great stuff!