I can't say enuff good things about running live plants. We run live macro in pretty much ALL of our setups. They look nice, and provide nutrient export, harbor pods, and provide refuge for fish. They also provide nice motion to the tank, and some fish and inverts eat them.
Most macroalgae such as Caulerpa sp. are very easy to grow and don't require bright lighting. In fact most of the red macros such as Botryocladia sp.actually color-up better under dimmer conditions.
True seagrasses (mantatee grass, turtlegrass, star grass, etc.) require very intense lighting as well as a minimum 4" sandbed.
A few pix:
Well, there WERE pix, but between SWF and Photobucket's "improvements", apparently it ain't gonna work...