Jasper is a popular tool. BIRT is an Eclipse.org tool. Google found JasperReports vs BIRT. I have no hands on with either of these (spent all day with Cognos Report Studio though) so I can't get you much further than the buzzwords.
A good question is never answered. It is not a bolt to be tightened into place but a seed to be planted and to bear more seed toward the hope of greening the landscape of the idea. John Ciardi