I am using APC UPB10 which was priced $60 at Circuit City. Here is the spec:
Capacity: 10WH (2000 mAh @ 5V)
Output Power: 8W (1.6A @ 5V) continous, 10W (2A @ 5V) peak
Although its capacity is no match Lil' Sync and Proporta, it nearly same size of a Samsung Blackjack. Pretty slim so I can slip it in my jacket without anyone notice.
When travelling, I use it with a very small 4 port
USB hub (4cm x 4cm) to charge different things at the same time, and store them in my bag.