When I got my TT-01, I bought [link=http://www3.towerhobbies.com/cgi-bin/wti0001p?&I=LXASX3**&P=7]this[/link] for it. It comes with two servos, so you'll have an extra. You could wait a while and they'll have one in stock with one servo instead but it only saves you a few bucks...so you may as well get this one and have an extra servo for a rainy day.

Anyway, I'd recommend it. It's worked well for me and it's not very expensive.