Blues News has spotted an interview on a Russian web site that reveals plans for not only a second S.T.A.L.K.E.R. expansion, but for a full-blown sequel as well.
The website - whose name my keyboard just can't reproduce - had an interview with GSC's Sergey Grigorovitch, where he reveals plans for a second standalone expansion to the game. Given the awesome name Call of Pripyat, it's due in the Fall.
Grigorovitch also mentions a full-blown S.T.A.L.K.E.R. sequel, but doesn't provide any further details other than the fact the team are working on it.