The website Clara posted is a good place to start.

Don't leave your dog with a trainer or at a training facility, you should be able to attend and participate in the whole process. The trainer is actually teaching you how to teach your dog. If a trainer says they use "unconventional" methods, run. If a trainer's methods make you uncomfortable or the trainer gives you a bad vibe, end the session. Different dogs require different methods of training. Some dogs learn well in a group, some need more one-on-one. Some only need correction and praise, while others are more treat/toy motivated. Prices will vary from trainer to trainer, but for your basic obediance it shouldn't cost an arm and a leg.