Have you ever had to figure out what version of Exchange a build number is referring to or vice versa? There is a very handy TechNet article that lists every build number and release date since Exchange 4.0.837 (Exchange Server 4.0 Standard Edition, June 11 1996)

Bhargav Shukla also has a great script that can be used to find Exchange 2007 and Exchange 2010 build numbers in your environment.