Swiftech MCX478-V Heatsink
There are a total of 374 pins aluminum alloy pins inserted into a half-inch thick CNC machined C110 copper bottom. Base dimensions measure 3" x 3" x 1.66". You'll notice this is very close to the inner dimensions of the stock P4 bracket. In other words, the cooler fits perfectly into the bracket and because it's almost the same size, it doesn't wiggle around. This eliminates improper/uneven installations. Total specified weight is 620g - not light but not nearly as heavy as the larger all-copper heatsinks.
And here's the link: