Check out The TORONTO STAR's wonderful online neighbourhood map. You can type your address into the search bar and it will show you the name and boundaries of your neighbourhood. This map is much more extensive and accurate than the summary neighbourhood map recently adopted by MLS and discussed below.
  

MLS replaces old district zones with neighbourhood names

On July 5, 2011, the Toronto Real Estate Board launched a new district structure to replace the existing TREB zones. This is intended to improve the search capabilities within the MLS®, and move from a district mapping system based on a “zone” identified by code numbers to one identified by commonly known names and more easily understood geographic areas.

In place of the old areas (Central, West, East and North) and districts (e.g. C01, C02, C08…), the new three tiers of address criteria will include Area, City and a Community (Neighbourhood).

The Toronto neighbourhood boundaries mirror those in the City of Toronto's neighbourhood maps, which you can see here: http://www.toronto.ca/demographics/profiles_map_and_index.htm.

Here's what TREB's new central downtown/midtown Toronto map looks like: