I actually have a complete water cooling information center shield coming out in a month or so. It displays temp from 2 bits power temp fittings so you get real time loop temps. You can add up to 3 more temp probes anywhere you want.
It also displays Pump RMP, Liquid Flow rate, PWM Fan speed control Up to 6 fans and 60w per channel, and it will display the rpm for each fan. I have added in an alarm (both visual and audible) to notify you of a drop in flow and am working on adding a RGB LED controller for those moders out there. The first revision is going to be a shield, the second will be a stand alone unit running an atmega 1280.
I have most of the project documented on my site if you are interested. http://themakersworkbench.com and have an article up in the arduino playground on how to read the RPM of common 3 wire PC fans.
Nice work!!