I want to know whatever heat source you guys use.

I use Flexwatt Heat tape with Helix thermostat.

Some advice: Buy a good thermostat. Yes they are pricey, and right now it may not seem worth the money, but I guarantee you it will save you a lot of headaches.

If you are starting out, I'd recommend a Ranco or Johnson thermostat from Reptile Basics. They are around $80 pre-wired, and work very well. I have also heard very good things about the Herpstat and Helix thermostats - they are more expensive, but also more accurate.

I use 11" flexwatt on all my tanks and tubs - it is very cheap and I have never had any problems using it. Just be sure they are wired to a thermostat.

I second a good thermostat... basically any heating system will work as long as you have a good thermostat. That includes lights and CHEs; after all, where does heat come from in the wild?

I never knew Zoo Med made a heat pad the size of Africa ;)