What is the best simple, portable power pack?

Do you have a recommendation for an (affordable) portable power pack, the kind that can jump-start a dead vehicle battery and power A/C off it? Basically a portable car battery. I had a Statpower Portawattz for the last 10 years that has served me well, but I am looking to replace it. It was around $100 +/- and looking to stay in that range. Thought you all might be able to recommend a brand.

Eric Wallace
Research Specialist, University of Arizona School of Natural Resources