I haven't had a chance to dig into these, but it appears that there are some "unofficial" mashups out there created by the folks at eMusic. There is a Pandora mashup which includes:
New Features in this version:
New eMusic browser tab at the bottom of the page monitors the track “now playing” and automatically displays the closest corresponding eMusic album page, artist page, or similar artist page
New “Recently Played” tab keeps a running linked list of the tracks & artists played/mashed
New “eMusic Radio Charts” tab highlights eMusic content receiving heavy airplay on various online radio services
Also, there is an iTunes (mac) plug-in that lets you select an artist from you library and "create station" in Pandora. Others also seem to be in the works:
Coming soon: More radio stations to choose from… KEXP, Seattle; WFMU, Jersey City; Soma FM, Last.fm, Selected Shoutcast stations, etc.