I would be using this for a commercial purpose so that basically rules out iText.
iText is available under a business-friendly license as well; check their web site.
FOP looka interesting but what are its known drawbacks?
FOP makes sense if the data is in XML format already, or can be transformed into XML w/o much effort. But you'll need XSL-FO skills, and not many people have those since it's not used all that much.