Non OW specific

http://kvs.unrealnetwork.com (KVS support thread) and
http://www.expertflyer.com/ - to check OW fares (may be more up-to-date than official OW sources) and availability.

http://matrix.itasoftware.com/cvg/dispatch - to check on whether one should use a ONE segment or pay for a segment separately.

great circle mapper - working out unofficial distances, anywhere in the world (reasonably accurate)

amadeus

seatcounter availability tool