I would definitely go with rails 3.0. Most of the plugins you will want for a new project, while being new to rails, will be available in rails 3.0.<p>There's quite a few of good stuff in 3.0 that makes it a lot easier for new people to get started, lots of improvements to ease usage.
Rails just released 3 today as a final release, which means its the new official release supported by the Rails team, so you won't have to worry about lacking useful plugins. In fact, rails 3 has MORE plugins built-in to the ecosystem than its predecessors.
I'm still working with Rails 3.b4, but I've found Rails 3 to be awesome. Very stable for beta code, even. ;) I hope to update to the release version in a few days, and update some older projects too.
Also, if it helps, rails tutorial ( <a href="http://railstutorial.org/book" rel="nofollow">http://railstutorial.org/book</a> ) is updated for version 3. This is a pretty good resource when you are just starting out with rails.