Radio Shack sells a silicone-based thermal paste that's cheap, readily available, very "wet" and easy to spread, and a breeze to wipe off so the CPU can be cleaned up for photos (another important consideration for me). However, it basically doesn't work well enough; a Pentium 4 will begin thermal throttling with this stuff inside of 15-20 minutes of intense computational load. Throttling will invalidate hours upon hours worth of benchmark results if you don't catch it early on, as I've learned through excruciating experience.
Then you have your standard gray and white goos. The gray goo is killer effective, but it's very thick, which makes it hard to work with and difficult to clean off. It ain't cheap, either. The standard white zinc paste works well enough, generally, though not as well as the gray stuff in my casual-but-experienced estimation. It is much easier to clean off than the grey goo, so long as it doesn't dry out. Firms like Antec sell white goo in teensy quantities in little plastic baggies for more than I care to pay, as if it were an illicit substance. I need lots of it, so I suppose I need to find a way to buy it in bulk, directly from the Colombian cartel.
Arctic Silver and its ilk are pretty effective at transferring heat, but they are also electrically conductive and damn near impossible to clean off. That nasty combination scares me enough to disqualify this stuff.
I recently picked up some Arctic Silver ceramic paste for a great price from TR sponsor PC Pitstop. The ceramic paste isn't electrically conductive and does its job very well. Although it's kind of thick, it does spread, and it can be wiped off fairly completely without too much effort. With a little use, though, it darn near turns into glue. Have you ever pulled a processor out of its socket in the process of removing a heatsink? I've done it twice in the past week, with an Athlon 64 3500+ and a 4000+. The first time, the 3500+ was so firmly bonded to the heatsink that I had to pry it off with a screwdriver. When the bond finally gave, the 3500+ went flying, dropping to the floor and bouncing around off of various bits of equipment, bending pins left and right. An entire outer row was bent inward at nearly 45 degrees, the tops of the pins touching the pins on the adjacent row. I wasn't born to be a surgeon. I spent what must have been an hour bending pins back with the empty tip of a mechanical pencil, and even now, the thing barely fits into a CPU socket.
Ceramic paste: great for LGA775 Pentium 4s, no good for socketed processors or BGA-mounted GPUs.
And my quest continues...
On an entirely different subject, we are now taking sign-ups for the TR fantasy baseball leagues. Pop some 'roids and join the fun.