I like to start things off by handing them a short piece of moderately crappy code and having them critique it. You get a good idea of how they think. We also kicked around the idea of showing them a function and having them write a unit test for it, or vice-versa. Never actually tried that though. And google docs would be a fine tool for the job. Wouldn't want to use it for day-to-day coding of course, but it should work OK for an interview.