I used Zen alot in the past, but I switch on and off every 6 months (for obvious reasons) so I may have to examine the market in a week or so. That said, Zen's always seemed to have good support when needed, gave me a fixed IP and didn't have much down time. Cancelling and opening services with them is straightforward.

Slightly off topic - anyone got Wii Mariokart yet? Wondering how it compares to Snes, 64 and Gamecube versions (yes, I'm that old and yes, I've played that much mariokart)