I'm a big fan of PartySpace.com - I found my venue on there! They have tons of venues for all kinds of weddings, including brunch receptions. They have unusual places too, that I didn't see advertised elsewhere. Here is the Philly link: http://partyspace.com/philadelphia
Check out Jeffrey Miller Catering! They offer a ton of venues with different days, and time of day options available. Brunch is definitely more affordable than a full sit down dinner.
I second the Jeffrey Miller suggestion! We're getting married at the Audubon center in a few weeks and it'd be a great daytime venue. They have lawn games they'll put out and other outdoor activities, which would be great for a brunch time reception.
Re: Brunch Reception