Well, if you want the absolute best (performance wise) 120mm and 140mm fans. The new industrialPPC fans from Noctua are the way to go. While most fans spin at 1200rpm, or 1500rpm if you're lucky. These fans spin at 2000, and 3000 rpm. Twice and sometimes nearly 3 times the performance. NOT meant to be quiet at all, these are meant for the highest possible performance.
Oh and also these have a much, MUCH nicer color scheme than most of Noctua's beige/poop brown fans.
Here's Noctua's product page, just scroll down and you'll see the 120mm and 140mm industrialPPC fans:http://www.noctua.at/main.php?show=produkte&lng=en
Oh..and uh...don't expect them to be cheap...