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.
Founded in the murky past (2007), YouMail lets you organize limitless voicemail greetings and assign them to specific callers, re-unleashing that killer Van Halen riff on anyone who "knows what to do". The process begins when your free account starts cataloguing missed calls, numbers you'll turn into contacts along with imports from Yahoo/Google/Outlook etc; once your contacts library's amassed, you can browse thousands of pre-recorded presets, from a variety of office standards, to classic movie quotes, to song spoofs, to authentic no-longer-in-service tones sure to stymie relentless harassment from...your mom. If you don't find what you need, upload your own MP3/WAV files, or use the provided voice recorder to create a fully personalized greeting -- unless they happened to catch the rerun on TBS, Fox, or the WB, no one will know you stole it from Costanza.
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!"