I've been researching CO2 also for my plants. Right now I dose plant ferts with excel (liquid carbon, the simplest way to add carbon). I just bought a desk light from Home Depot for my 2.5 gallon. It's the Hampton Bay Desk Lamp with 27 watts, 6,500k. I dose excel everyday and I am hoping to see good plant growth with this light, the ferts, and the excel. I'll have to report back to you in a few weeks if I see good growth.
I heard that injected CO2 (more difficult than liquid carbon) is more readily available for the plants to use than liquid carbon. I just didn't want to get too technical with my setup (But I might still do it anyway). You can find 'How to' videos on youtube and go on the plantedtank.net to see how to make one. The most difficult part to this setup seems to be getting the CO2 bubbles to defuse into the water properly. I read that the CO2 diffuser needs to be placed where the water returns from the filter to help 'chop up' the bubbles.