I have bought a number of GForce batteries from Value Hobby: http://www.valuehobby.com/power-systems/batteries.html So far, I have been happy with the balance between quality and cost for these.

Also, watch for sales on Gens Ace batteries at HobbyPartz: http://www.hobbypartz.com/gensacelipo.html I have a few of these too and have no complaints and they do run specials from time to time.

I have heard many horror stories about Hobby King, but I have never had a problem with them myself. In fact my oldest batteries are a set of Rhinos I bought from Hobby King 5 years ago that I still use every season. The most expensive batteries I ever bought were a set of Thunder Power packs I bought at my LHS, one of those puffed after only two seasons of fairly gentle use.