The easiest way to get around Brussels is to walk. The city is small enough to hit up most attractions on foot.
To visit a few dispersed attractions in one day, it is best to use the STIB system, which is a mixture of bus, tram, metro and premetro (underground) lines.
More information at: www.stib.be.
One trip: €1.40
Five trips: €6.30
Ten trips: €9.20
Day pass: €3.60
Information at: The Brussels Airport Web site (Sometimes this very well designed airport site features specialty cartoons too!)
Note: All prices were accurate when compiled. Please check the Web sites listed for the most up-to-date information.