Tuniq TX-2 [silicon oxide grease]
This is what I use.
OCZ Freeze [aluminum oxide]
Arctic Cooling MX-2 [aluminum oxide]
Noctua NT-H1 [silicon oxide grease]
I’ve seen this one recommended for those who have a phase-change cooling solution, as the Tuniq stuff apparently will not work with it.
Arctic Silver 5 [polysynthetic silver]
The disadvantage of this one is the 200-hour curing period necessary before it will perform at its best. I used to use this one.
Notes:
For heatsinks with a copper base, it is advisable to avoid using silicon-oxide-based pastes for best results.
I myself have done no testing, and these results are primarily for my own record, having read many reviews on different products. I saved the results of my (incomplete) research into a spreadsheet, and I have 3 different versions available for you to download: OpenOffice “.ods” (recommended - 20KB), Excel “.xls” (71KB), and CSV (6KB).
FYI: The lines highlighted in gray mean that my research is not complete for those particular brands.