The Nano-tech lipos that hobbyking sell are very nice, although the Gens Ace lipos on hobbypartz.com have also been getting very good feedback; comparable price and specs:
http://www.hobbyking.com/hobbyking/s...dProduct=11940
http://www.hobbyking.com/hobbyking/s...dProduct=11936
http://www.hobbyking.com/hobbyking/s...dProduct=11957
http://www.hobbyking.com/hobbyking/s...dProduct=11955
http://www.hobbypartz.com/98p-40c-50...-hardcase.html
http://www.hobbypartz.com/98p-30c-5300-4s1p.html
http://www.hobbypartz.com/98p-25c-5500-4s1p.html
Quality of the regular flightmax and turngiy lipos is fine, so long as you stick to the higher C rates & dont get a bad pack with a weak or dead cell- same old issues with iffy QC.
That said, the G2 packs Kershaw Designs is selling have gotten some good feedback too, but they only come in 2 or 3s flavour:
http://204.186.93.64/Batteries-LiPo.htm