Right now the 64mm market is a bit limited to a handful of lightweight fans, the GWSEDF64 is one of the original and still the best overall in sound, efficiency and performance, the Wattage powerfan is more aggressive in pitch but can sound very cool in the right applications, then you have all the knockoffs which look very much like a GWS, many of them work quite well and perform with almost the same figures.

I build the EDF64 with our ERC2445 inrunner, performance is very good on 4 cells, it pulls 38A on the bench, 42A with ducting, pushes 1.1kg thrust. Here is a video of a quickly knocked up fan to test.
[youtube]http://www.youtube.com/watch?v=Qf6x1YzlR1c[/youtube]

There will be a new option very soon, I will have a new 64mm alloy fan to add to our Extreme Alloy lineup, it will feature a pretty serious rotor and will take 28mm motors, performance should be at the top of the 64mm tree. Weight will be kept as low as possible with hi grade alloys and fine wall thickness.