For the list if BizTalk system properties that travel along with messages in the system, you must use that system-properties namespace. Found here: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/sdk/htm/ebiz_sdk_msgcontprops_oydf.asp.
For the list of other BizTalk Global Property Schemas properties go here: http://msdn.microsoft.com/library/default.asp?url=/library/en-us/sdk/htm/ebiz_prog_proj_pjqr.asp