Harmony Kendall - Buffy / Angel
The Chosen One: Mercedes McNab played the vapid and self-obsessed teen cheerleading queen Harmony, second only to Cordelia, before graduating to play the vapid and self-obsessed teen vampire Harmony throughout the rest of the series, eventually moving onto Angel.
Her Stake in Things: After shuffling off that pesky mortal coil, Harmony went on to annoy the underworld as a vampire, particularly her undead sometime-love interest Spike, who attempted to stake her with more than just his...ahem. After failing miserably as a villain, Harmony moved onto sunny (for humans, anway) Los Angeles, taking a secretary position with Wolfram and Hart. And sure, she might have betrayed Angel in the end, but what woman could resist Adam Baldwin?
Leaving Los Angeles: Mercedes hasn't lost her taste for the demonic, appearing in both Supernatural and the short-lived Reaper.