agree with alexwuk: but better use the GERMAN opodo site www.opodo.de
there are 100s of websites doing tix in DE, and prices hardly differ. Use google.de. A point to note, when booking from OUT of DE is, that many tr-agents simple wont take CrCd for payment (this is germany).
IF you want to save money check DATES; it may differ over 100% between low and high season
Generally nonstop flites cost a little more as transits, but to/fro US on US-carriers this hardly matters