Davane: I am pretty sure that 1998 or 1999 is going to be Baldur's Gate - It is the defining RPG of the genre. I would have said Fallout for 1997, but GOG.com can't distribute that any more...
I'd go with Myst for 1993, Syndicate Plus for 1996, Dungeon Keeper for 1997, Total Annihilation for 1998, Deus Ex for 2000, and Evil genius for 2004.
These are just some of the biggest games I recall from my past 30 years, and the dates may be off by a year or two, and it depends if they are celebrating when the game came out, or when the expansions we done. Lots of leeway, either way!
Do you have any guesses for the year 2006 and 2009? I'm curious to know what you think. :)