As a recent Villanova alum (which is where I gather you're going, based on your signature), I recommend reaching out to Home Properties of Bryn Mawr, an apartment complex nearby the school. So many Villanova students live there (mostly seniors, who are forced to live off-campus) that the University runs a shuttle there between the hours of 8 am and 9 pm. While I'm not sure they have a list of people looking for roommates, they should be able to point you in the right direction; one of the administrators in particular is extraordinarily helpful, although I forget her name.
It's a bit pricy compared to most places of the country, but the Main Line is going to be expensive no matter what, and it is close to the Norristown High Speed Line.
If you have any questions about the area, feel free to PM me! Not only did I go to Nova, I was also a History major as well!