Ed Peters has the list of the current College of Cardinals, arranged by the date on which each will turn 80 years old and thus become ineligible to vote in a conclave. Two will drop off the list by the date of the consistory—bringing it to the limit suggested by Pope Paul VI of 120—and seven more this year.
If we estimate that consistories take place on average every two or three years, 11 more will age out of the list by the middle of 2008 and a total of 25 of the 120 will fall off the list by the end of 2009, barring any deaths of course.
As of March 24, using the current list of new cardinals, there will be 120 cardinal-electors. By the end of June 2008, there will be 102 cardinal-electors. My guess is that another consistory will happen by then.