prolly something like this would work
http://www.marinedepot.com/md_viewIt...product=EJ1119
You want about 3-5 watts per gallon is usually the rule of thumb. I think mine is a 150w and around 90g of water volume.
I tend to go on the less is more side since I don't want my tank to cook just in case something happened.
Best thing to do is get 2 lower wattage heaters and if one goes crazy, it's not strong enuff to cook the tank. Otherwise look into getting a controller.
Personally I think the Ebo heaters *in the link* are the best ones around- many people seem to like them and I've heard stories of them lasting 20 years. I don't trust any other brand.