This is one of the best shows on television right now, but unfortunetly I have heard rumers that it is being cancelled.  This show is a spin off from Buffy the Vampire Slayer and Buffy along with other cast members have made appearences, but not recently since Buffy went off the air.
Show Background
Angel was sent to Sunnydale to help Buffy defeat the Master, but he fell in love with her and he stuck around. He and Buffy got really close and it appeared to be too close because when they did he lost his soul and tried to kill everyone Buffy loved. Eventully Buffy had to kill him, but he came back and stuck around only until graduation day when he moved to L.A to continue his work.

This is the original cast of Angel. When the show first started Doyle showed up with his visions and told Angel that the higher powers selected him to help angel with his destiney. Cordelia, who was a stuck up little rich girl on Buffy went to L.A. to start an acting career, but before long she was in need of recueing. She thought she was going to hit it big, but the man who said he could help was a Vampire that just wanted a meal. Angel runs to the rescue and Cordelia hired herself to work for Angel's Investigations. It wasn't too long before Doyle gave his life and his powers of preminission to the battle against evil. Cordelia  received Doyle's powers and it was a rocky road, but good prevailed and Angel continued to save the innocent for 5 season, but sadly they have decided to cancel at the end of season 5.
CAST
David Boreanze
ANGEL
James Marsters
SPIKE
J. August Richards
GUN
Andy Hallett
LORNE
Alexis Denisof
WES
Mercedes McNab
Harmony
Amy Acker
FRED
Vincent Kartheiser
CONNER
Carisma Carpenter
CORDELIA CHASE
Glenn Quinn
DOYLE
The Bad Guys
Christian Kane
Lindsey
Daniel Dae Kim
Gavin Parks
Gina Torres
Jasmine