We really need more information to give you a good answer.
If you want fast growing plants, then you will need Co2 (I would recommend a pressurized system for this tank size for ease of maintenance) and possibly daily dosing of ferts. This also required higher light as well. Do you want to go with Compact Florescent's or T-5's? With CF's just as as guide, I might go for something around 120w, and with T-5's maybe around 80w, both with excellent reflectors.
If you want a lower maintenance tank with slower growing plants, then you might be able to skip the Co2 altogether and go with something like 80w CF or 60w T-5.
Don't let the prospect of Co2 turn you off from planted tanks, or even what's often called "High Tech" tanks. Planted tanks are a carefully balanced system, and can be interesting to learn how each part fits and interacts with the next.