The (private, liberal-arts) college I attended has for many years now had a fairly striking imbalance; currently it's 59% female and has been hovering around that 60/40 mark for at least the past decade, if not more.

Edit: the US Census bureau provides data. Most recent figures (http://www.census.gov/population/www/socdemo/school/cps2008....) show 10.3 million female college students to 8.3 million male college students.