The comventional wisdom has been that Chief Justice Rehnquist would announce his retirement from the court in the next week or ten days.
The Weekly Standards Bill Kristol offers what he calls informed speculation that Sandra Day OConnor will announce her retirement in the next week and that Alberto Gonzales will be nominated to replace her. Kristol speculates that Gonzales will be slightly more conservative than OConnor and that Rehnquist will announce his retirement when OConnors replacement is confirmed. He expects Gonzalez to be named Chief Justice at that point and a hard core conservative to replace Rehnquist as an Associate Justice.
Heres a MainStreamMedia report on the top candidates for a Supreme Court replacement.