A post over at Shell Games on the list of former Terps in this year's MLB playoffs got me wondering about how many Terps were in the Major Leagues this year. There were two in 2010: Justin Maxwell, a Center Fielder for the Nationals (.201 BA, 16 H, 15 R, 12 RBI in 67 games) and Brett Cecil, a starting pitcher for the Blue Jays (15-7, 4.22 ERA in 28 starts). Additionally, Kevin Hart is signed with the Pirates, but was out all season after shoulder surgery in May (the team says he should be ready to play again by spring training).
Maryland's baseball team site has a list of all the Terps who made it to the majors with stats updated through 2009. Notably, Ron Swodoba won a World Series with the Mets in 1969, Vic Keen won with the Cardinals in 1926, and Charlie Keller won in 1939 and 1941 with the Yankees (and played in two other World Series in 1940 and 1942), and was selected as an All-Star five times.
Here's a more comprehensive list of Terps in the Majors from Baseball-Almanac.com that goes back further and has more names. The additional names seem to be players who only played in a small handful of games at the major league level. (Also, this list incorrectly shows several players as Hall of Famers; I double checked, and none of them are in Cooperstown.)