First, make sure your lights are pointed even with the driver's field-of-view, not down at the ground or up at the sky.

For commuting, I use a cateye EL320 and this sucker is bright. It is around $40, new for 2006/2007. I think I might prefer it over my $250 niterider digital for city riding.
http://www.cateye.com/en/product_detail/325

I also have a nashbar tiny light set inconspicuosly mounted on the helmet. When I really feel like I need to be seen I'll turn on the front helmet light in blink mode as well as whatever else I have set up on the handlebar. Since this light shines in the direction that I'm looking, I have better control of it.
http://www.nashbar.com/profile_moreimages.cfm?sku=18354