DB2 is incredibly underrated outside the "large enterprise" crowd. It is a truly awesome RDBMS with bazillions of cool features (and a somewhat ugly Java UI). It has the equivalents of most of Oracle's features and has the scalability of Oracle while being both more user-friendly and considerably cheaper.

Its response times for simple queries are not exactly stellar though so I wouldn't recommend it for simple CRUD websites. But for serious data heavyweighting on a budget, DB2 Express-C (the free edition) is excellent.