I received email the other day about a newish service called rVibe-Live that streams concerts live over the internet. They're also accumulating a nice archive. I was alerted to two chamber music concerts at Bargemusic, the Brooklyn series that takes place on a barge moored in the East River. You have to create an account, and I'm mildly confused that the email talks about buying tickets, while the web site says "free and easy." Maybe creating the account is free and you pay for individual concerts.
I have not tried it out; if you do, please let me know how it goes. The next streamed Bargemusic program is this Saturday, February 21, at 8 p.m. EDT, String Trio in NYC.