Generally, we're talking about a maximum of 12 volts and maybe 40 milliamps with the Arduino. Not in these projects.
Arduinio Nixie tube shields
Nixie tubes are awesome. They're old technology, but they appeal to almost every kind of electronics aficionado. They require high voltage to run. They look cool. They're tubes -- they've got so many awesome points working for them. For someone who doesn't know how to build the electronics to push them though, they're basically off limits.
A couple of shields out there are specifically built for running Nixie tubes from your Arduino.
The Arduinix Nixie tube shield is an open-source product that enables you to power and control Nixie tubes directly from your Arduino. It can take your standard 9V Arduino voltage and bump that up to 250 V to power pretty much any Nixie tube you'll find. It also has a nice feature of multiplexing, which should help prolong the lives of your precious tubes.
Open-source Nixie tube via Kickstarter
An open-source Nixie tube shield that recently had a successful Kickstarter campaign is also quite nice. The ability to plug directly into an Arduino and run enough tubes to have an hour, minute, and second display is especially well thought out. Unfortunately, we don't see any way to order these. Maybe you could contact Tyler Nehowig, the creator, and ask to purchase one.