Possible additions:
I suppose Baldurs gate II (2 million I think) could be on the list although Neverwinter Nights and Dragon Age are spiritual successors.
Duke Nukem 3D is another possibility although there were other Duke games, none were FPS and it did have a number of expansions. Not sure on full sales numbers
Counterstrike could possibly be added to the list. Although there have been updated versions and an engine upgrade, they're essentially small updates to the same game (Counterstrike 4.2 million, Condition Zero 2.9 million, Source 2.1 million, not including Steam sales as of 2008, 1.5 million on X-box) .
Goldeneye? I know a remake has now been announced and Perfect Dark was a spiritual successor but it's another possibility (8 million sales I think).
There are some problems with your current list though:
Diablo 3 has been anounced, possibly next year.
Flight Simulator?! 1996?! There have been like 10 versions since! But, the last one came out in 2006 and Microsoft don't look to be making another. Not sure how well it sold.
A new Doom is apparently in development. Think it was revealed they were working on it at Quake-con a few yrs back?
