Aeroplan (Air Canada) lets you build stopovers into long-haul trips that can give you a "mini round the world" trip for 75-80K points per person (economy) or about 150-155K per person (business class). Two years back we did Toronto-Lyon-Istanbul-Bangkok-Hong Kong-Osaka-Vancouver-Calgary-Toronto (the only long stopovers were in Lyon, HK, and Osaka). Then, as Malacca suggests, you can build in cheap local side trips from your longer stopovers.
For details and advice (including how to avoid most fees), check out Flyertalk>Aeroplan>mini-RTW.