Not much can beat the AE5's for fan controlling in a water cooled system mate. I've had one AE5 PRO, then an AE5 LT, and now back to an AE5 PRO.
The thing to bear in mind about fan controlling for a watercooled setup is that conventional fan controllers don't control the fan according to water temperature - this is whats needed in a watercooled system (The strength of the AE5)
The AE5 products give you unbelievable control over the fans - for example this is my setup:
System temp - according to this my front and rear intake fans are adjusted.
Water temp - according to this my top radiator fans are adjusted.
You can also set start and end RPM's for your fans - excellent for noise control.
Further to this you can also check water flow, pump speeds etc - provided its all hooked up. You can even control LED's (so for example light your PC internals according to how hot it is! lol).
Awesome product - Even though the software is in BETA its very stable and literally all things work - running it on Windows 8 now - worked straight away
don't forget to buy an in-line temp sensor (only air temp sensors are included with it). I've got 4 in-line temp sensors so I can monitor at four differents points in my system (Water Res, Graphics, Rad in and Rad out), also got a air sensor, and a koolance flow meter to monitor flow rate. Prob OTT but essential when I can't get to see inside my PC as its rammed between the desk and a wall.