Re: your JDBC wishes: Consider IBM Cloudscape (now Apache Derby) too,
which has an apache license. It's all pure java and it's easy to get going.
As to MySql vs Postgres: license issues aside, if you have
transactionally complex needs (multi-table updates, etc), PostgreSQL
wins hands down in my experience. There are a bunch of things about
MySQL that just suck for high end SQL needs. (I like my subqueries,
and I absolutely demand transactional integrity).
There are some pitfalls to pgsql though, especially for existing SQL
code using MAX and some other things which can really be blindsided
(performance-wise) by pgsql if you don't use the workarounds.
MySQL is nice for what I call "raw read speed" applications. But that
license is an issue for me, as it is for you apparently.
Some cloudscape info:
http://www-306.ibm.com/software/data/cloudscape/
Some info on pitfalls of MySQL and PostgreSQL, an interesting contrast:
http://sql-info.de/postgresql/postgres-gotchas.html
http://sql-info.de/mysql/gotchas.html