Try this link to get a picture of the best type:

Fitness Shop - Boxing, Martial Arts, Fitness Equipment, Thai Boxing, Karate, Kick Boxing, Weights Bench, Punch Bags, Bag Stands, Gym Equipment

Stay away from anything that attempts to cover both breast with one piece of plastic or padded material.

I haven't actually owned the type above but have been frustrated by the other trypes available. They mess with your movement too much and make you look like Madonna - especially if your local boxing association has you competing in male style singlets with huge armpit holes! It's not pretty!

The big padded ones I've found make it very difficult to keep you elbows in and the hard plastic ones with elastic are slightly better but move and don't breathe and are still not comfortable.

I had a training partner who owned and recommends the soft sports top type with protective cup inserts and it did look comfortable and easy to move in.

Sop around - i think i've seen ones which are a better shape than the one pictured in the link attached but that's the basic idea anyway!