Prepared by James Mitchell 1/16/2006
Here is a list that will hopefully give you good information about Philadelphia. I've annotated it based on a quick scan so I cannot vouch for all the content.
Community Information - Philadelphia City Guides
Good summary information with lots of links to other sites. No specific real estate information. Focus is on the city proper, not the suburbs.
The Official Visitor Site for Greater Philadelphia - FAQs
Aimed at the short-term visitor rather than someone moving here, but still has decent links covering the wider (PA only) region.
Moving to Phildadelphia - From Wharton School
Aimed at Penn's Wharton graduate students but still has some good advice.
Center City Residents' Association
Exactly what its name implies, a site for residents of Center City - the "hot" area to live at the moment. It's not particularly helpful in finding a place to live, but will give you a sense of the environment.
Neighborhoods of Philadelphia
This gives a good characterization of the neighborhoods in the city - it looks pretty accurate from my scanning of it. It does not address the suburbs or NJ.
Philadelphia Neighborhoods - Links to a variety of sources
A guide to the neighborhoods of Philadelphia and the surrounding five county metropolitan area.
Covers a lot of informatin, mostly about the city itself. Seems to be pretty good.
Philadelphia Neighborhood Information - AOL cityguide
I'm quite impressed with what they say about the specific neighborhoods, it seems factual and helpful.
HousingMaps - Very helpful Google Mashup
You can put in your price range and see what's being offered (complete?) where, often with pictures. By playing with it you should pretty quickly be able to locate the "prime" areas of the region.
Relocation Information for People Moving to the Greater Philadelphia and South Jersey Area
Quite a few links that may be helpful covering the entire region.
Connecting Utilities Online
I haven't tried it, but it looks as though it gives useful information once you've decided on a residence.
Real Estate Classified
Not much help deciding where you want to live, but should be helpful getting a sense of what's available and how much it costs.
Community Calculator - Find location like one you know well
This is a superb idea, well implemented. You enter the zip code of a place that's like what you want. It gives you a list of similar locations within 50mi of the city you identify. You get good demographic information as well as acces to information about schools. This is where I would start when househunting in a strange city.
School Reports - Dig down to detailed school information
Very useful information about schools. You can dig down to very meaningful information. It's allied with the Community Calculator. Good stuff.