Fun fact I came across tonight while trolling Wikipedia:
An inside-the-park grand slam is the same event but, like a grand slam, features the bases loaded for an inside-the-park home run. There have been 224 inside-the-park grand slams in Major League Baseball history, 26 in the past 50 years, and only eight since 1990 (as of 1 August 2011). Honus Wagner has the most in MLB history with five.
The most recent player to hit this feat was Omir Santos of the New York Mets on March 7th, 2010, against the Washington Nationals.