Microsoft and Apple have probably the most extensive HCI resources out there. The problem is, developers working on OS X seem to treat Apple's work as a Bible, the developers for Windows treat it as more of a guideline, if they are even aware of its existence.
It is a shame. When I first started programmin for Windows, their HCI guidelines are a lot more comprehensive than Apple's, but they were expensive! I think they are free on their Knowledgebase now.
The Windows stuff used to be very comprehensive, including helpful box-outs in the documents about why certain things were done a certain way or things to think about when implementing them into your own programs.
Looking at the stuff that is coming out these days, it is easy to think that Microsoft never published any standards...
