Go cheap on the trainer. I have an earlier version of this one:
http://www.performancebike.com/shop/...egory_ID=4120# and it works just fine. It has 5 levels of resistance. Add in the gears on your bike and you can always find the level of resistance you need. The highest level is high enough that it will never become too easy, so you don't have to worry about that.
Buy an expensive trainer and you're spending a lot of extra money on something that's a little more quiet and has more of a "realistic" feel. My trainer isn't waking up the neighbors or anything (and you're probably going to be pumping up some music anyway) and no matter how "realistic" they claim to make it, it's still a trainer and you're never going to mistake it for an open road.
Buy the cheap trainer and spend the extra money on books and/or DVDs.