I'm no expert on accents or anything, but to my ears there are four easily distinguishable accent groupings in Toronto (not including those of transplants and immigrants), and at least another 4 in the rest of Ontario (in which I have a lot less experience however).
There's the standard, indistinguishably North American bourgeoisie accent. Standard among the educated, upper middle class and generally throughout the inner city...basically like most any North American within this demographic. (this is my standard sober accent)
There's the Italian-Torontonian accent. Similar to the gruff Italian-influenced accents of the northeastern US but with more Canadianisms. Y'know, "aboat" and stuff. It's a bit different than Montreal's Italian Anglo accent. (I tend to slip into this accent when I'm with family or when I'm mad)
There's the accent & manner in which most working class-middle class young people speak (under 30 or so)...not sure what to call it, but it's basically the Toronto equivalent of the Multicultural London English
accent, I guess. Lots of different influences (I would group the above-mentioned Jamaican-Canadian accent into this, for example), and often "unique" phrases, but it's unmistakably Torontonian. As much as I'm unable to describe it, it's something I've never heard outside of Toronto. Most prevalent in the inner suburbs, but it seems to be working its way into the inner city and the inner portions of the 905 (Mississauga, Brampton, etc.) as well. (this is how I sound when I'm around my old neighbourhood pals and/or when drinking)
There's also the still-present older variation of the working class-middle class inner suburban accent: think Mike Myers in Wayne's World. Seems to perhaps hold on to a bit of the old Irish influence, resulting in something sounding sort of half way between a Maritime accent and an Ontario accent. I can always identify it by the stressed a's - "But I still know how paahrty!"
And then there's the typical, Don Cherry Southern Ontario accent which works its way into the edges of the GTA.
In the rest of the province, you have the more nasally, American-sounding Southwestern accent, the Ottawa Valley accent, and then of course the classic Bob n' Doug Northern Ontario accent.
It's a bit tough to describe this sort of thing, but that's my best attempt anyway. I'll maybe look for some videos or audio clips later. (okay, I'm not actually going to do that)