4sysops published an extensive, 9-parts article on different application virtualization products available on the market.
The piece covers the common features of all products listed in the virtualization.info Virtualization Industry Radar (plus the OEM’d LANDesk Application Virtualization), also reviewing a couple of them (Symantec/Altiris SVS and Xenocode Virtual Application Studio) in details.
If you are looking for an overview of this technology this article is a good start.