I've always read on here that heat pads aren't any good because they don't sense heat on their bellies and can get burned.
For temperature regulation, I have an IR temp gun for $15. You just point it at something and it will tell you the heat and we've tested it at work against their sensors and it is spot on. I've temped pretty much everything now, and it's worth the $15 just for fun ! I temp my soup, my cats, my co-workers, and more !
For the actual source of heat, I have a 75w halogen bulb in a dimmable dome fixture. I had to dim it slightly to get the desired temps, because on full tilt it went to 120F (but there wasn't anything at the store between 50 and 75, and I thought the 50 might not be enough). The dimmer is great for controlling temperatures very precisely. The dimmer saves you having to try a bunch of bulbs until you find the perfect one - which can get kind of expensive with halogens.
What size is the tank, and what's the ambient room temperature ? My room is 67 degrees and the 75w bulb slightly dimmed works well for a 50 g tank, although I need a second bulb for the "cool side" because it doesn't get as warm as I'd like. When he was in a temporary 20 long, I used a 100w regular household bulb which achieved the desired temperatures - but did not in the bigger tank.