● iMac (Mid 2007 or newer)
● MacBook (Late 2008 Aluminum, or Early 2009 or newer)
● MacBook Pro (Mid/Late 2007 or newer)
● Xserve (Early 2009)
● MacBook Air (Late 2008 or newer)
● Mac mini (Early 2009 or newer)
● Mac Pro (Early 2008 or newer)
If you are wondering why older 64-bit Macs cannot support Mountain Lion, Ars explains:
Information included with the first Mountain Lion GM now corroborates the connection to 32-bit graphics drivers as the culprit. While Mountain Lion is compatible with any Mac capable of running a 64-bit kernel, the kernel does not support loading 32-bit kernel extensions (KEXTs). Furthermore, Macs with older EFI versions that are not 64-bit clean won't load Mountain Lion's 64-bit only kernel.
Hit the link below to see the full tech specs for Mountain Lion.