I know alot of guys are probably going to recommend Turnigy. I've come across enough evidence that they perform great out of the box but don't last before they degrade, puff, limited number of charge cycles. My buddy has taken them apart and said the build quality on the Nanotech version of them is crap... soldering etc. Many people get them with dead cells right out of the box. My buddy said the regular Turnigy are actually better built and I've seen many others say that as well... but, they're still Turnigy with some of the same pitfalls.
I know the posts will come in saying "I haven't had any problem with mine" ... I'm staying away from them, personally.
I haven't used them yet, but I bought some Gens Ace... I use the brand in my surface RC's... perform as good as Thunder Power and last as long... alot of guys swear by them and will use nothing but them when organized racing. Have seen some evidence of QC issues on those as well but not as much. You can get this size (1300mah 25C) for about $24 direct out of china from sdshobby... hobbypartz if you're in the U.S. and they're even cheaper there.