Hi there,
since you already got the JAA CPL/IR, passing the respective FAA knowledge tests should be "a piece of cake". The FAA tests are pretty much straight forward and by far not as abstract and extensive as the JAA BS! If you are just looking for a QDB, I can recommend the following website, they are for free!
Pilot Practice Page
Webexams.com
FAA Written Exam Test Preparation for Pilots
FREE FAA Pilot Tests Prep Center
FAA Written Test Prep for PC, iPhone/iPad, and MP3 players. Current for 2013! (Pay-ware!)
If you are looking for a little more (including CDs and/or ground instruction on CD) check-out the following two links:
ASA: FAA Test Preparation (check-out the virtual test-prep)
Pilot Ground School | King Schools (John & Martha King very famous among the FAA Aviation community - good stuff)
Hope I could help!