I have a 55gal and use a 100w. I think most people suggest 100w, but you could wait for some other answers. The three top ones are powersun, megaray and trex. From what I hear, megaray and trex are the best and give off the most heat. since you have a big tank, you might actually want to get a seperate LOWER wattage, household bulb to put a little more heat on the cool side of the tank. If this confuses you, I'll post a pictures of how mine is set up. The important thing about MVB's is the distance! They need to be at least 12 inches away from the basking spot. Let me know if you have any other questions. The best place to buy the mvb's are on petmountain.com, they have the lowest prices.