For the current project I am on we are using MySQL which is a pretty good DB. SQL Server is still a bit more advanced with it's capabilities, but MySQL is getting more impressive with each release. I would highly recommend it for anyone who doesn't want to pay MS's high cost for SQL Server. I am talking, of course, about someone using a Windows environment. For Linux, there is no other choice ... MySQL is the way to go.
I've seen flame wars in regards to DB's I know alot of people are hard core postgre and supposedly it does benchmark better than MySQL for many task..