Well, despite members of the Resident Evil: Extinction cast saying otherwise, a fourth Resident Evil movie is definitely very much alive and currently being shot. According to Shock Till You Drop, they've received confirmation that a Resident Evil 4 movie is currently set for a September 17th, 2010 release and will see the return of Alice and her army of clones. Also, Jessica Chobot of IGN's Daily Fix was kind enough to reveal that the Resident Evil 4 movie is rumoured to be set in Alaska and Tokyo; while this has yet to be officially confirmed - IGN is normally pretty reliable when it comes to this sort of thing.
Update: Just to make everything absolutely clear: I am not saying there will be a Resident Evil movie based on Resident Evil 4. I am merely stating that a fourth Resident Evil movie is in the works.