I bought a pair of spoke lights last year. When they work, they're great. However, they eat through batteries very quickly. I'm getting reflective tape and putting it on my rims and a few other strategic spots. It's the most economical solution, I think. If I get anything thing else for active lighting, it might be a couple of these, which I'd attach to the frame (and wire to a 9V battery).

http://cgi.ebay.com/LED-LIGHT-TUBE-B...item5ad5d5cc89