in reply to
What is your favourite Linux or cross-platform database?
PostgreSQL (http://www.postgresql.org/, see also http://wiki.postgresql.org/)
- BSD license ( ultra-free )
- pgAdmin is nice enough; psql, the commandline client, is great.
- *very* active & helpful community; reported bugs often fixed within hours. There is often instant help at #postgresql / freenode.
- SQL:2011 ( see: SQL Conformance )
- ultrareliable: yes
- DBD::Pg (see: DBD::Pg )
Postgres is supported on a wide range of platforms (see the distributed buildfarm status page (which continually tests if compiling is still faultless) - not even all platforms are represented)
SQLite is only good for 1-person use, and then only with limited data size (the SQLite website honestly admits this). It is therefore IMHO not really a serious candidate for the epithet 'database', but YMMV, and you can see from the other replies that the opinions vary as well. SQLite is also good for embedded use, where postgres is not usable.
update: Added mild SQLite bashing & some wordsmithing.
update (2012.10.27): s/SQL:2008/SQL:2011/g;