Old South/Wortley Village - London - is probably the nicest neighbourhood I walked through this year outside of Toronto. I never used to think of it this way, having hung out here in the 1980s on weekends. Lovely old homes, a small village strip with a Valumart, yet reasonably close to downtown. I'm very tempted to buy a buff brick home here sometime.
In the GTA, downtown Burlington surprised me the most. Very vibrant with a great waterfront, many Victorian homes. Unfortunate that many of the newer condo towers are ugly, but they're bringing a density to the area that reminds me of Victoria. Although Hamilton has a larger core, Burlington feels more happening.
Finally, Stratford. Anywhere built pre1950s is fantastic. Stratford is the nicest small city in Ontario; Orillia in second place.