The biggest name in thermal compounds (aka TIMs or thermal interface materials) is Arctic Silver. They have been at it for a long time and are the most respected company in the game. Currently their two most popular products are Ceramique and, at the higher-end, Arctic Silver 5. The "Arctic Silver" line has been around for some time- it is the companies flagship thermal compound and is usually regarded at the industry's best. Note that the previous compound was AS3, as no AS4 was ever produced.