If you need advanced features, I would also recommend PostgreSQL. It's open source, reasonably well-known, and contains a lot of the standard features (stored procedures, views, triggers, etc.) Perl support is very good. However, my experience is that it doesn't necessarily deal well with huge data sets .. for that you probably want Oracle.

One thing to consider if you're a major Perl geek: MySQL either has or is developing a "native" programming language (similar to PL/SQL or PL/PGSQL) but based on Perl. I haven't worked with this myself, so I can't vouch for it, but it's a data point to consider.

Hope this helps.