The web site I like to use is:
http://www.jimkaras.com/loss_math01.cfm. This gives you an AMR and a recommended calorie level to lose 1 pound per week.
Another web site is
http://www.room42.com/nutrition/basal.shtml. This gives both BMR and AMR. I don't usually refer people to it, though, because it recommends going under your BMR to lose weight.
Keep in mind this is only an ESTIMATE which assumes everything about your body & metabolism is "normal." But, it's a good place to start.