(just edited this post - formatting got screwed up when using Google Chrome browser)

I had to learn about Agile approaches in March this year when I was thrust into the role of project manager for a startup firm.

I found the following very useful:

Agile & Iterative Development by Craig Larman for a broad introduction to all the well known methods including Scrum, Extreme Programming, Evo and the Unified Process - I found this very useful for understanding the principles and background

You might also find these helpful:

Agile Estimating and Planning by Mike Cohn (fairly obvious what this is about)

Agile Retrospective by Esther Derby and Diana Larsen. The retrospective is a powerful concept for reviewing and refining the prior iteration for subsequent iterations. There are a whole series of techniques in here which are of broader application to the analyst for prioritisation of requirements and generating requirements etc

Try a website with free articles for newbie and practicing business analysts - www.businessanalystmentor.com

Another good resource is the AGILE TOOLKIT podcast, which is full of interviews with all the big names of Agile.