Simpliest and cheapest and prob one of the easiest to use - Astro Blinky -

http://www3.towerhobbies.com/cgi-bin...&I=LXMRZ9&P=ML

This works either as a standalone balancer or a while you're charging. You plug it into teh balance plug on your lipo. While charging, the balancer makes all cells have teh maximun cell voltage of 4.2v. Used as a standalone, it discharges all cells down to the lowest voltage indicated by any cell.

You get a better charge by balancing while charging.