Some of the shows there are syndicted (not owned by Sirius), such as Alan Colmes, Ed Schultz, Thom Hartman, and Young Turks. Those guys stream or offer downloads of their shows on their own sites.
Lynn Samuels streams her show from the Sirius Left site. Hers is the only one streamed.
Alex Bennett, one of their newer hosts, is trying to arrange streaming of his show. I sent him a message on a newsgroup he frequents asking if he was going to stream, and he said that Sirius is open to the idea, and they're trying to work it out on at least a temporary basis. Haven't heard anything as of late.
For now, he has put up some streaming files on his site, both of his Sirius show and his fill-in work for Lionel:
http://www.radiofreejack.comGreat listening. He's a left-leaning libertarian who loathes Bush.