The Fractal Design Celsius S24 is actually pretty cool - you can unscrew the fittings and daisy-chain units. I wish more AIO's would let you do this, what do you think? :
Fractal Design Celsius S24-240 mm Radiator - Silent Liquid CPU Cooler - PWM - Intelligent Controls - 2x Fractal Design Dynamic X2 PWM GP-12 120Mm Silent Fans Included - 1/4" Fitting - Black : Amazon.it: Informatica