Some database odds and ends:
1) The DotNet Rocks podcast recently had an episode with David Simons. He went over 10 different database systems, ranging from relational to NoSQL. Slides from his presentation are available on Slideshare.

2) A couple of free E-books – Free but they requires setting up a login or filling out your contact information:

A. Time Series Databases: New Ways to Store and Access Data by Ted Dunning and Ellen Friedman
An intro to storing Time-Series data (recording a value over a period of time)

B. MarkLogic – Enterprise NOSQL For Dummies
A basic overview of NoSQL and how it compares to a RDBMS

C. Some database-related books from Syncfusion – These are 100 page books (PDF or Mobi) that are great introductions to a topic:

3) I’ve added a Database Systems page to list and link to open source relational and NoSQL database systems. I’ll update this list periodically.