It's kind of a hit and miss process. 1500 is what Jillian Micheals always recommends starting out no matter what, then once you figure out how your body works you can adjust it from there.
I saw a dietitian early this week and he said the BMR and weight loss calculators at Livestrong.com were actually pretty good.
Kelly, you are right, but I was told (by the dietitian) that that only remains true as long as you are significantly overweight. Once you start nearing normal weight, ESPECIALLY if you have gotten into an exercise routine, you have to completely reconfigure it to account for a bajillion different things that i'm not completely sure of right now. My BMR is about 1200 a day, but I exercise. Eating 1200 cals a day had my body in starvation mode for the last seven months. I'm eating around 1800-2000 since Tuesday, and sure enough just in the last four days i've lost a pound.
So DRose, no matter what you do now, remember that it won't work consistently unless you plan on just relying on diet and no exercise whatsoever. It may also turn out that it's ineffective after 20lbs or so, so the best thing to do is keep track of it and always be ready and willing to adjust. It's confusing, but you can do it.