Depends on what "reasonably affordable" is, and how much you believe in the idea that cool has no price tag.
Just to start off, here are some of the things I have found.
LED underbody kits. Made for an ATV but can be used on a bike. Note that Google will turn up many more hits for "LED under body kit".
http://www.ledunderbody.com/Million-...hting-Kit.aspx
LED valve caps - require presta adapters.
http://www.niagaracycle.com/index.php?cPath=286
Spoke lights.
http://www.hokeyspokes.com/index.html
More spoke lights
http://www.monkeylectric.com/
If you are OK with DYI projects
http://www.instructables.com/id/Spok...-Wheel-Images/
Really, there are a lit of options available.