go with overhead heat sources. When the lights turn off at night, turn on a red bulb to keep a hot spot somewhere. If you don't put vents in the cage (or only put a small vent, as I did), you'd be suprised how well one 50 watt halogen bulb can heat up a 4'x2'x2' enclosure.
My uromastyx enclosure is on the floor, where ambient temps can be as low as 60-65 degrees ambient temperature with the lights off. With the lights (a single 50 watt halogen and one of those 7 watt twist in flourescents to add light to the cool side), I get a hotspot that reaches as high as 160 degrees (I put a rock down, and then put corkbark on top of it, so she can choose to bask on or under the cork bark depending on how hot she wants to be). The ambient temperature of the hotside is usually around 80-85 degrees, with the ambient temps of the coolside being more around 70-75. Those are just about perfect temperatures for uromastyx. Good hot basking spot, and nice mid-low ambients.
The bearded dragon enclosure is similar, just that I added another vent in because his cage was actually getting too hot. I was trying to use another 50 watt halogen bulb, but that was getting too hot, so I switched to a 75 watt zoomed basking spot bulb, which produces less heat, and gives me a basking spot that ranges from about 105 to over 120, depending on the kind of day (sunny days warm my room more and overcast days keep it cooler).
Also, give some room in the enclosures for dirt. Especially the uromastyx. Go on www.proexotics.com and see what they say about keeping uromastyx. If you have the ability to keep the uro on a lot of dirt, do it! They love to dig burrows, and having an area of high humidity to retreat to is a necessity!