Hey Doc
What size tank do you have, and how much light do you have going into your tank?
Right off the bat I'd say get a Java Fern. They're pretty much bullet-proof. I'd also recommend Java Moss, but I've never had any. Everything I've heard or read about it tells me it's bullet-proof too. If your tank has been set up for a while and your gravel is not overly big a crypt (wendii or becktii) or a smaller anubias would work. They're all fairly slow growers, so you can keep up with them very easily.
If I knew what kind of light you had, I'd reccommend some aponogeton bulbs. You can get them at Wal-Mart.
You don't really need CO2, but at your higher light levels it helps the plants out-compete the alge.
But, what do you have that you want to pitch a plant into? ???