My boyfriend is bi and I must agree with you when you say that it's a huge turn on. Up until him I had been worried about having a male bisexual partner (jealousy issues and such), but I truly love it about him.
My current boyfriend is straight but I have been with bi men in the past. I always kind of enjoyed it. It was a turn on...and we could check out guys together. They also seemed to have less jealousy issues than straight men I've been with.