Hey Vincent,
First, Tom's advice was well-meaning, but not good advice - don't just pick a database because someone says it is the best - do your own research as you will be married to the DB once your projects get more involved and it becomes prohibitively tedious to change a DB later. Also, Postgres is a jack-of-all-trades DB that does almost everything; there are purpose-built DBs that may fit your project better and are usually far easier to use and scale than the jack-of-all-trades style (like Postgres or MySQL)
If you want a full overview of many of the most-modern SQL (eg. Postgres) as well as NoSQL (eg. MongoDB) databases, check out the videos of the various DBs on
http://www.DatabaseMonth.com
Also, consider attending tomorrow's Database Month event which has free BEER, Pizza, Swag- New Operational Database: Scale-out Transactions & Real-time Analytics, presented by Sergei Tsarev, Co-Founder & CTO, Clustrix with Dmitri Mikhailov, Principal Database Architect, TheLadders