Hope this helps!
People's Choice Realty
There are a number of websites that offer open house information, including Realtor.com, Century21.com and HomesofPennsylvania.com. Other sites that might help are Trulia and Craig's List. You can also try the websites of your local newspapers, including the Philadelphia Inquirer and Main Line Times.
Let me know if you have any other questions... good luck!
One great place to look is http://www.weichert.com. You may search for open houses, choose the ones you want to see, and then click "create my tour" to map out your route. Also, you will find some open houses advertised on http://www.craigslist.com and http://www.philly.com. Happy hunting!