metal halide
As you can see from the other replies, there is an issue with heat, but as long as you keep the MH far enough away from the top of the tank it shouldn't be a big deal. 6-12" would be about right. I have been playing around with them for a few months, I'm currently using a 175W over a 37 gallon tank to get it growing before putting in the animals, and the plant growth is great, the Tillandsia ionathas are all pink and flowering, the orchids are blooming, basicly the plants are doing great, and the light or associated heat aren't hurting anything, though I plan on using a 70watt Iwasaki 6500K bulb when I put the animals in.
One aspect of MH that I like for larger tanks is you can put it on one end of the tank, then the animals have a temp and light gradient, so they can go wherever they feel comfotable. The light also penetrates the "canopy" farther. I think I prefer the color rendering of the CF's better though. I've tried several MH bulbs with CRI's in the 90's and the CF's seem more balanced color wise. Another thing to note is that the CF's, particularly from 55watts up, are more efficiant than most halides that would be suitible for viv use.
Good luck, have fun