Give Dr Bronners liquid castile soaps a try, if you haven't allready. Great stuff!! A little goes a long way. I buy the big bottle for home use, and pour off small portions for trips. Works very well and is economical.

-Can be found at REI, Whole Foods, Wallgreens and likely others. Cheapest place I've seen the big bottle was REI, maybe 3 or 4 bucks less than Wallgreens (at the time).