This week's book giveaways are in the Refactoring and Agile forums. We're giving away four copies each of Re-engineering Legacy Software and Docker in Action and have the authors on-line! See this thread and this one for details.
McKoi DB seems pretty fast but is still an up-and-coming product. I would definetively recomemnd HSQLDB or the recently released CloudEscape (don't remember the Open Source name). Axion is still not quite ready for production use.
Co-Author of <a href="http://www.amazon.com/exec/obidos/ASIN/1590591259/ref=jranch-20" target="_blank" rel="nofollow">Enterprise Java Development on a Budget</a>