H2 database rocksDecember 02, 2006
I've been working with H2 for several months (in fact all my blogs run on it) and its been fast and dependable. I noticed that Thomas just released the official version 1.0. Give it a try.
You wouldn't want to run Ebay on it, but for many uses its far better than MySQL (better SQL support), PostgreSQL (much faster) and certainly a better bet than his first DB, HSQLDB , which I have also used in the past.