Alex Rodriguez will likely break quite a few more records before he's through. However, his grand slam tonight -- tying Rodriguez with Lou Gehrig for most all time (23) -- might be one of the more difficult records to take away from him.
To break a home run record, you need to be a prodigious home run hitter. Solo or multi-run, it doesn't matter. To hit 23 grand slams, you need the opportunity to come up with the bases loaded on multiple occasions over your career AND be that prodigious home run hitter.
Manny Ramirez has 21, but as he languishes in the Oakland minor leagues, it's no sure thing he'll get a crack at joining the Iron Horse and A-Rod. The aging Carlos Lee (16) has the next most among active players, and is the only other active player with at least 15 grand slams.
Here's A-Rod talking about the accomplishment: