YouMail
Voicemail greetings are impossible to nail -- too professional, and prepare for taunting messages from friends; too creative, and prepare for taunting messages from your now ex-employer. Please everybody, with caller-specific greetings from YouMail.
YM also offers email alerts with embedded vmail audio, letting you reply via text/email, and has a transcription service in beta, so when you accidentally select the "Chicken Dance" for your boss's greeting, you won't even have to hear him say "YOU'RE FIRED!"