In the "modern era" (since 1901), only five players have played at least 2500 games at first base.
Answer after the jump later today...
UPDATE -- I just realized I screwed this up. I should have said, played at least 2500 games, with at least half of them at first base.
I'm stupid. Sorry.
There are still just five, though.
UPDATE II -- Answers are now up after the jump.
Murray, Palmeiro, McCovey, Buckner, and Perez.