XP/Server 2003
ApplicationData: C:/Documents and Settings/<user name>/Application Data
CommonApplicationData: C:/Documents and Settings/All Users/Application Data
CommonProgramFiles: C:/Program Files/Common Files
DesktopDirectory: C:/Documents and Settings/<user name>/Desktop
LocalApplicationData: C:/Documents and Settings/<user name>/Local Settings/Application Data
MyDocuments: C:/Documents and Settings/<user name>/My Documents
ProgramFiles: C:/Program Files
System: C:/WINDOWS/system32
"Program%20Files"
Vista/Win7/Server 2008
ApplicationData: C:/Users/<user name>/AppData/Roaming
CommonApplicationData: C:/ProgramData
ProgramFiles: C:/Program Files
CommonProgramFiles: C:/Program Files/Common Files
DesktopDirectory: C:/Users/<user name>/Desktop
LocalApplicationData: C:/Users/<user name>/AppData/Local
MyDocuments: C:/Users/<user name>/Documents
System: C:/WINDOWS/system32
"Program%20Files (x86)"
PS. This list is not exhaustive, it's just a few I've come across.