Microsoft Windows Server 2008 (64-bit)

You couldn't ask for more, or for less. Windows Server 2008’s fine-grained, modular configurability lets you shrink the OS footprint down to virtualization guest-friendly size, and Server Core drops the Windows GUI to dramatically reduce the memory requirements of a virtualized guest. This server OS presents a minimal attack surface for guest and host instances, and generally removes the requirement for add-in server and client security. It isn't a server in a box, but it's Microsoft’s richest server OS by far.» Read Full Review

8.5 Very Good

Manufacturer: Microsoft
CostStandard: $999 with 5 CALs, $1,199 with 10 CALs; Enterprise: $3,999 with 25 CALs; Datacenter Edition: $2,999; Windows Web Server 2008: $469
Platforms32- or 64-bit AMD or Intel x86 or Intel Itanium CPU, with minimum speed of 1.4GHz. Memory and disk requirements vary by edition and features. Author's recommended minimums for Windows Server 2008 Standard are 1GB of server RAM per virtual instance and 40GB of local hard disk for boot and swap. The GUI-less Server Core's requirements are much lower.