Visit the Official SAT Question of the Day website here or just subscribe to the question of the day.
Other recommended resources for the SAT:-
Cracking the SAT with DVD, 2011 Edition (College Test Preparation)
11 Practice Tests for the SAT & PSAT, 2011 Edition (College Test Preparation)
McGraw-Hill's 12 SAT Practice Tests with PSAT, 2ed (McGraw-Hill's 12 Practice Sats & PSAT)
Know of more SAT preparation materials that you've found useful? Do share them here!