Packet8 kicks Vonage's ass.
http://www.packet8.net/
We've been using them for over 6 months now with no issues at all.
Packet8 had a local number for our area, and Vonage didn't.
Packet8 also offers the ability to send you an email with attached sound file when you get new voice mail. No extra money. And no extra charge for caller ID, call waiting, 3-way calling, etc.
They are cheaper than Vonage, and we can make unlimited free long distance calls to the US and Canada.
When we signed up, we took the special which includes a Uniden Whole House VOIP system which has a base unit with built-in router, and a handset. We're very happy with it:
http://www.packet8.net/about/uniden.asp