Sergey Grigorovitch, GSC Game World president, revealed in an interview that we can expect to see a second expansion for S.T.A.L.K.E.R. in the stores this autumn. Its title will be "Call of Pripyat", but maybe even more interesting is the fact that he brought up that they are currently working on S.T.A.L.K.E.R. 2, as well. No further details about S.T.A.L.K.E.R. 2 were disclosed, though.
S.T.A.L.K.E.R. - Shadow of Chernobyl was originally released in 2007 with an expansion, called S.T.A.L.K.E.R. - Clear Sky, following in 2008.