Where can I see what will be on Sirius?
DogstarRadio.com has the full SIRIUS schedule in a tv guide style format.
Where can I see what song I'm listening to?
Where can I see what song I heard earlier?
ItsOnSirius.net allows you to search playlists by song and artist title. They also allow you to see what was played on a particular channel over the last five hours.
itson.siriusbackstage.com also allows you to see what is now playing and search by song or artist. In the past they have supported advanced searches and reportedly will again.