There was a brief period when Singapore Airlines and Bristish Airways offered joint service between LHR/SIN. The Concorde was painted with both SIA and BA colours and logos. You can view the photos at airliners.net. Sadly this service was very brief. As far as charter flights, there have been many. I seem to recall the Concorde being in Vancouver for Expo 86 and having flights to nowhere. I also believe during that time there were one or two trips to HNL from YVR.
Please see a new thread I have started about talks of a new Concode being discussed between the French and the Japanese.