Better then AS-5? Try the Innovation Cooling (IC) Diamond 7-Carat Thermal Compound (uses diamonds since they offer the highest thermal conductivity of basically anything. Much more so then silver or copper).
Oh, and how about some proof:
"It seems that there is definitely a more than viable alternative to Arctic Silver 5 on the market place now. While the results weren't jaw dropping they certainly were impressive and warrant your attention. Five degrees Fahrenheit is a respectable drop and we weren't the only ones to attain that...
I'm using the IC Diamond 7-Carat Thermal Compound my self, and it works as promised.
Ultra M998 mid-ATX case
SilenX 650W 14dB SLI Power Supply Unit
Nvidia/EVGA 780i tri-SLi motherboard
Intel Q6600 quad core @ 3.4GHz (3.6 for benchmarking)
2GB OCZ ReaperX HPC Edition PC9200 DDR2 RAM (2x1GB)
2x EVGA 9600GT SC in SLI (750/1100Mhz over-clock)
2x WD Raptor HDD (1x 36GB; 1x 74GB)
Samsung Spinpoint HDD (250GB)
Thermalright TRUE-120 w/ dual 120mm fans in push-pull config.
Windows Vista Home Professional w/ SP1 (32-bit)
Samsung SyncMaster 206BW 20" LCD display (1680x1050)
3DMark06: 17,420 Points