Buffy the Vampire Slayer
Although Cordelia started off as a self-involved character, she grew throughout the first three seasons, learning to love others (spawning a relationship with Xander Harris, above). After Season 3 of Buffy, Cordelia moves away to L.A. to become an actress. After having little luck, she meets Angel and they work together in the detective business- Angel Investigations. Cordelia's character grows even further throughout Angel as well, and by Season 4/5 of Angel, she seems to be a completely different person.