With Senator Mark Kirk's (R-IL) recent statement, there are now 50 U.S. Senators (48 Democrats and two Republicans) who support marriage equality and 50 who have not yet evolved.
As Josh Israel at Think Progress notes, "with Vice President Joe Biden the tie-breaker, this marks the first time that a majority in the U.S. Senate has endorsed same-sex marriage."
Democrat holdouts are: Joe Donnelly (D-IN), Tim Johnson (D-SD), Heidi Heitkamp (D-ND), Mary Landrieu (D-LA), Joe Manchin (D-WV), Bill Nelson (D-FL), and Mark Pryor, (D-AR).