What I really like about Curves is that it's very goal-oriented (which is good for me, because that's how I work), but it's also really health-oriented. The emphasis is more on losing fat than on losing weight, and once a month they take various measurements (your waist, hips, bust, arms, thighs, etc.) and your BMI. I haven't lost much weight, but I have lost two whole points on my BMI since I started (though that was before I went home for two weeks for the holidays -- eep). It's also fairly inexpensive as gym's go, though I have a student-rate that works a little differently. And it's very low pressure and friendly (mine is, anyway).
Anyway, just thought I'd let you guys know this is out there. It's the only thing I've found in years (besides riding my bike in Germany) that I've managed to stick with for more than about two weeks.