Hey Dani,
According to reviews, the best bang for around $100 is the ThermalTake BigWater SE. You can get it for about $114 at ZipZoomFly. Reviews say it's virtually silent, and performs better than the loudest air-cooled solution. It's good for stock speeds, and mild overclocking.
I'm putting one together now, and will report on my experience. :withstupi
If you want max performance and/or custom looks and fun, you'll have to spend at least $150 for a do-it-yourself high-flow system, and be prepared to spend some time collecting parts and converting a automobile heater core for radiator use. If you want that high-flow system to be near-silent, you'll have to pay $75 for a super-quiet high flow pump.
Hope this helps, and stay cool!