Kevin (a.k.a - SDB) didn't say it, but I will. Buy a SportDog collar and don't look back. I used a Tri-Tronics before getting my SportDog SD-2000 last fall. I love my SD collar.
Though I have not had a lick of problems with my collar, a few people have in the past. This is not to imply they have many problems, they don't. But just like every company out there, occassionaly an inferior product reaches the consumer. Every single one of the users that had a deffective collar that I have either personally talked to or read about has had nothing but positive comments about the customer service at SportDog. You can feel confident that buying a SportDog collar is a lifetime investment.
The SD-2000 collar sells for $279, much cheaper than many of it's competitors. However, you might also look at the SD-400 for about $149. This is a collar with less range but all of the features of its big brother.
Last thing I would like to say is work with someone who has collar-conditioned a dog before. Watch their dog and make sure they are happy to have the collar on, this is a pretty good sign that the dog was collar-conditioned in a positive and humane manner. An e-collar is a great training tool, but can easily be abused. If you have any questions about using the collar, this is a great place to ask.
Roger