As far as bang for the buck, I don't think anything beats the A123 cells. DeWalt packs can be had for $110 and will net you 10 cells. A little time on your part and materials and you can have two 5s packs (that will perform simialarly under load as 4s lipo) for $125.
I have some of the 8AH TrueRcs as well. They are really nice, but they are just a bit too wide @50mm fit everywhere. Other than that they are great.
I like the idea of hte A123s too, just they are a bit too big and heavy and low runtime for me to take the plunge with them now. The next gen ones should be really awesome tho. They have great potential.