I struggled to find this info. Basically these keys make your pc's/server activate from your KMS server, you could need these if you were switched from MAK to KMS and want to move the MAC clients to the KMS server. Just change the product key in System and it should try to find your KMS server.

Vista
Windows Vista Business
YFKBB-PQJJV-G996G-VWGXY-2V3X8

Windows Vista Business N
HMBQG-8H2RH-C77VX-27R82-VMQBT

Windows Vista Enterprise
VKK3X-68KWM-X2YGT-QR4M6-4BWMV

Windows Vista Enterprise N
VTC42-BM838-43QHV-84HX6-XJXKV


Server 2008
Windows Server 2008 Datacenter
7M67G-PC374-GR742-YH8V4-TCBY3

Windows Server 2008 Datacenter without Hyper-V
22XQ2-VRXRG-P8D42-K34TD-G3QQC

Windows Server 2008 for Itanium-Based Systems
4DWFP-JF3DJ-B7DTH-78FJB-PDRHK

Windows Server 2008 Enterprise
YQGMW-MPWTJ-34KDK-48M3W-X4Q6V

Windows Server 2008 Enterprise without Hyper-V
39BXF-X8Q23-P2WWT-38T2F-G3FPG

Windows Server 2008 Standard
TM24T-X9RMF-VWXK6-X8JC9-BFGM2

Windows Server 2008 Standard without Hyper-V
W7VD6-7JFBR-RX26B-YKQ3Y-6FFFJ

Windows Web Server 2008
WYR28-R7TFJ-3X2YQ-YCY4H-M249D


Windows 7
Windows 7 Professional
FJ82H-XT6CR-J8D7P-XQJJ2-GPDD4

Windows 7 Professional N
MRPKT-YTG23-K7D7T-X2JMM-QY7MG

Windows 7 Enterprise
33PXH-7Y6KF-2VJC9-XBBR8-HVTHH

Windows 7 Enterprise N
YDRBP-3D83W-TY26F-D46B2-XCKRJ

Windows 7 Enterprise E
C29WB-22CC8-VJ326-GHFJW-H9DH4


Windows Server 2008 R2
Windows Server 2008 R2 HPC Edition
FKJQ8-TMCVP-FRMR7-4WR42-3JCD7

Windows Server 2008 R2 Datacenter
74YFP-3QFB3-KQT8W-PMXWJ-7M648

Windows Server 2008 R2 Enterprise
489J6-VHDMP-X63PK-3K798-CPX3Y

Windows Server 2008 R2 for Itanium-Based Systems
GT63C-RJFQ3-4GMB6-BRFB9-CB83V

Windows Server 2008 R2 Standard
YC6KT-GKW9T-YTKYR-T4X34-R7VHC

Windows Web Server 2008 R2
6TPJF-RBVHG-WBW2R-86QPH-6RTM4