If you're on an extremely tight budget, this light -- http://www.dealextreme.com/details.dx/sku.18307 -- is remarkably good for $7.43. Unlike most of DE's dedicated bike lights, this light is actually well put together, and it's pretty bright. Really, my only problem with it is that it takes 4xAAA cells, when I'd prefer 2xAA cells like the Planet Bike Blaze 1w.

It puts out roughly the same amount of light as the PB Blaze 1w, but lacks the exceptional flash mode. (But it has a standard flash mode, so if you're into those things you've still got it.)

Not that it can compare to the P7 lights we all like so much, but you can't beat it for the price.