Best newbie / advanced / expert reference texts for Git?

[Dun Peal <dunpealer@gmail.com>]

Hi there,

What are the best texts for the following three levels of knowledge:

1. Newbie: someone who used a simple, centralized SCM (such as SVN)
but never touched Git.
2. Intermediate: someone who uses Git's simpler features, and can do
simple branching/merging, but would like to fully understand the
underlying concepts such as the DAG, and master all common user-level
operations such as branching, merging, and rebasing.
3. Advanced: someone who knows all the above, but would like to know
everything there is to know about Git.

The target audience in my particular case is smart, with strong CS
background, especially those in the two latter categories.

Being available online is a plus, but will not disqualify a good
offline reference.

Thanks, D