What aquarium plants should I choose to have?

I have a 20 gallon aquarium and I want to grow some live plants that are hardy, pretty, completely aquatic and require a moderate or variable lighting. Nothing that grows to big either. I need more hiding places, so a plant that can give me that would be great. Any suggestions? I have a regular gravel (not nutrient rich) and no driftwood, but i can get some if my perfect plant requires it.