Korth wrote:
It's Thermal Interface Material (TIM), commonly called Thermal Paste or Thermal Grease.

ASUS (and every other manufacturer) uses standard industrial-grade cheap-in-bulk TIMs. You won't be able to find exactly replacements, but premium-grade TIMs are commonly available and fairly inexpensive. You'll find a lot of premium TIMs on the market though. Aggressive overclockers want only the best of the best. Many routinely repaste their devices, automatically disdaining the factory goop in favour of their own preferred TIM brands.

Every premium-branded TIM has zealous champions, there are many online comparisons/reviews which rate "laboratory" benchmarks of TIMs side by side. The truth is that any premium TIM generally outperforms the ASUS standard TIM but the ASUS goop was also good enough for the job, some people claim great (even outrageous) improvements in their temps after repastes but I always read their numbers with some skepticism, the ASUS goop can be certainly upgraded but it's also not the component which usually bottlenecks cooling performance.

I would recommend Arctic Silver 5 for the "paste" and Startech Heatsink Thermal Foam for the "pads". The whole idea is for the TIM to fill the void between mating surfaces, but also to use as little of it as possible since even the best possible TIM goop isn't as thermally conductive as the metal heatsinks it's joining. AS5 is not always the best-of-the-best-of-the-best but it's always in the top-tier performers, it's cheap and common and general-purpose, and (unlike most other branded TIMs I've tried) I know it'll last at least a few years between applications before it all cooks off.

Just as important as the choice of TIM is the application of TIM. Not too much, not too little, full even coverage. Sometimes this requires a different TIM with a different viscosity or properties for optimum heat transfer between different surface geometries, the very best possible thermal performance might even require multiple TIMs on different parts of the same machine. It pays to read some guides and watch some vids about processor or graphic card or laptop repasting, but again I would take most of the reported (usually biased) numbers with a little skepticism.

I recommend avoiding "liquid metal" and "phase change" and "reflow" TIMs on first-time applications. Focus on learning how to apply the TIM correctly but be realistic and allow for the possibility of having to re-apply it after less-than-satisfactory first attempt(s) - the exotic TIMs have different application methods and, they're more costly and often only provide 1-2 applications and, most importantly, removing them (to clean the surfaces for new application) is a serious chore you will quickly regret.

navis995 wrote:
Instead of the grease go for pads as the result will be the same but less messy next time you'll want to repaste your chips.

Instead of grease for the die's use Liquid Metal like Collabrium Liquid Ultra, you'll see huge drops in temperatures.