My favorite sports bras are these Victoria's Secret ones. I have 3 of them, but I got 2 at a semi-annual sale and one online after quite a bit of searching. They're called Medium Impact sports bras. Extremely comfortable, plus they actually make your boobs look good rather than the awkward blob that a lot of sports bras give you. They look like this, though mine are pink, green, and white. http://www.polyvore.com/medium_impac...ng?id=14127179
I ride in a normal bra half the time, but I can't trot for very long before I have to stop because my boobs hurt.