I would have to say, either the Trakpower V-Balancer (Though leads for it can be a problem - though not if you look at Heli places - it's about £35) (
http://www.flighttech.co.uk/index.as...^item=TPVBAL2S), AND (
http://www.flighttech.co.uk/index.as...eries/EON.html - You need to click on 'Leads and Accessories' to find it)
Or the Logic RC Fusion Balancer - they do 2 types,
Up to 6S (
http://www.logicrc.com/?ItemId=O-FS-...0,c:40,c:40-40),
and up to 12S (
http://www.logicrc.com/?ItemId=O-FS-...0,c:40,c:40-40)
so you could balance charge up to 6 packs at once!
(If your charger can handle that though...). (The 6S one is also cheaper than the V-Balancer, and they include leads to balance both Flightpower packs, and most others (JST-XH type plugs)
I have the Logic RC 12S Balancer, and have to say it is very good. I have used the Trakpower / Flightpower (same thing) V-Balance, and it is a good piece of kit - probably the best on the market.