The exercise calculator doesn't factor in strength exercises

You can enter it under Cardio but it's an estimate at best (as with all the exercises in the database). I think that they don't put any calories under there because it's not really possible to calculate strength training calories burned accurately without knowing a whole lot of information. You can however use it to log what you did (sets, reps, etc).

You probably know this already but the best thing to do is to invest in a decent heart rate monitor. Much more accurate. I've recently picked up a Polar HRM & it's really helpful.

I list my weight exercises at the gym under "cardio", too. I also list my treadmill, bike and elliptical under "cardio". The weight machines are not cardio, but like you, I could not find a way to find it under strength. Sure, they are all estimates, but I like filling it in anyhow because it shows me the direct relatuionship between what I consume and my physical exercise. I do not always "eat" ALL my exercise calories, but sometimes I do. Mostly, for me putting in my exercise points is a very helpful reminder that I need to get out there and walk, or go to the gym if I want to keep eating more or less like a "normal" person, without gaining weight.