Like Jim, I like the PB Blaster (except for the fact it gives me a headache for some reason). It's great stuff. One other thing you can try if the PB Blaster doesn't work is use a small hammer to tap the bleeder valve a little (not real hard). That can sometimes break loose the rust that's down in the threads and allow you to loosen the bleeder. Before you get it out of there, I'd go to the dealer and grab a new one to put in its' place so it doesn't happen again. Take the old one out and use a small brush to clean out the threads, bleed some fluid out to clean out the junk then put the new one in. After you do it, you ought to bleed the whole system again to make sure you get all of the bubbles out.
P.S. As a personal preference, deep 5-point sockets are best for everything to keep from rounding off under pressure.