To Rails from Django
I'm in the same position as you: I need to learn Rails for work, and I was hoping to find an article/tutorial that expresses Rails concepts in terms of how they differ from Django concepts.
After a lot of searching, I found this:
http://www.vaporbase.com/rails-django
This compares the ways in which Rails and Django each implement various web development concepts.
It's very long and in-depth, but it's well structured so you can just dip into the bits you need help understanding.
One big downside, though: it was written in 2007. But it's still useful as long as you bare this in mind.
UPDATE:
I've also found this – a shorter, more up-to-date, cheatsheet-style comparison:
Rails Quick Start for Djangonauts
This one is good for quickly checking what terminology is used by each framework for a given concept.