You can get a combo pack, Blackburn Quadrant and Mars for about $30-40. The Quadrant is rather large for a 4-LED light, but I like that it has a dual-mode (2 steady, 2 flashing) as I'm a firm believer in having at least some steady light for reference - it's hard to gauge distances when all they see of you is flashing light. The Mars is also quite competitive for a taillight in the <$50 category. (read as: not a Dinotte)

Separately, I like the PB Beamer5 a lot, as well as the Superflash and the Flashpoint from Performance. Hope that helps!