The bar and club scene is Philly is alive and kicking!  Probably the most-popular (and revitialized) district over the last 10-15 years has been Old City (named aptly because it is Philadelphia's oldest neighborhood).  Some great bars and clubs in Old City include the following: 

 

32 Degrees - an Old City hotspot on South 2nd Street where they serve shots in glasses made of ice.  VIP Lounge with great (but expensive) bottle service.

Moda - Unpretentious and mellow hangout on Chestnut Street.  Good music.  Get a Moda Monkey, sit back and relax.

Club 27  - Located at 27 Bank Street, this one is mostly for the younger crowd.  Lots of popular dance music.  It is large, with 3 dance floors.

Anthony's Old City Pub - Right in Market Street, this is a great bar to go to if you don't want to get all dressed up and just hang with your friends.  Inexpensive drinks as well.

Swanky Bubbles - Located right on Front Street - great place for a frou-frou champagne cocktail with the girls.  If you're hungry, order up some sushi.

The Continetal - The first of the martini bars on Market Street in Old City by none other than Stephen Starr.  Get a Buzz Aldrin at the bar in the back.  Great drink and great ambience.

Lounge OneTwoFive - This is the place in Old City for hip hop, techno and house music.  Nice decor with couches, hammocks and even a waterfall.

Marmont - Located right on Market Street in Old City, you can't miss Marmont.  It has a very sexy look from the street and a really nice bar.  The potent Marmont Champagne Cocktail is very tasty - chambord, Stoli raz and bubbly. 

The Plough and the Stars - a great, upscale Irish pub in the heart of Old City.  Really nice in the winter to have a pint of the black stuff by the fireplace.

Sassafras - Right on 2nd Street, it's a true old-time classic bar, complete with a tin ceiling and tile floors.  Completely unpretentious.  Good beer selection.  Great prices.  If you get hungry, skip the "international fare" and order a burger.  One of the best in the city.

Yello'bar-in hip part of town (24th and Grays Ferry),it's a great neighborhood bar with good food and great array of beer on tap. Low key and eclecic group of people. www.yell-obar.com .  Free wi-fi available for those work vacations!

Philadelphia Nightlife Info    Philly's More Fun When You Stay Up Late