Depends who you ask, there are numerous people on here who believe that strap I was talking about is a huge no-no, and refuse to use anything but a harness with a single strap along the back connecting the neck and chest straps.
I have seen the damage caused by harnesses with out it on cats and other animals, and its just common sense to have a harness with that strap. Safer for the animal, less escape-able, and more comfortable around the neck. But just remember if your animal tries to run and flail and pressure is put on the leash and then onto the harness because their pulling into it, all that pressure will be solely on the strap circling the chest and circling the neck leading to 2 pressure points, the moment you add that 2nd strap that connects the 2 you turn that entire strap into the pressure point greatly decreasing the pressure on 1 single spot, as well as lowering the neck strap away from the trachea. You also make it harder for your rabbit to sneak their head out of the neck strap.
I know a few people here use the mesh vest small animal style harnesses.
I think I got mine in the cat section at petsmart.
http://www.petsmart.com/cat/harnesses/cat-36-catid-200081
They have lots of pretty colours to choose from. Not sure if mine is the Great Choice Cat harness or Great choice Kitten harness. I'm leaning towards kitten because my guys are only 3lbs....
But make sure it has an O ring where that center strap connects to the neck straps, that helps it form a V like in the photo I posted, otherwise it will still come up higher on the neck.