Aviator: one of the best and very popular. Sometimes too rigid for a little birds comfort. Fits tight over head getting it on. The only thing I don't like about it is that you cannot take off the leash, so if your training inside your house, you have this big long cord following your bird around. Not that big of a deal I suppose.
Harness by Fred Bird that I can't remember the name of:
Very good harness also. Still rigid, but easier to put on than Aviator with removable leash.
Flightsuit: Has birdie diaper if you care about that. Rest of it is a nice shape and softer for your tiel. Leash could be longer.
Jungle Vest: Like the Flightsuit, but with no diaper. Less material for your little bird, and still soft. The Flightsuit has better shoulder straps, and this one is a little smaller. I wish they had the Flightsuit without the diaper. I'm currently working on one of my tiels to wear the Jungle vest. I wish the leash was longer, but I might make my own if I can ever get it on him.
Good luck!