I haven't had access to enough of the privates to give comprehensive advice but what I have played or seen (including St. George's, Weston, Islington, Scarborough, Devil's Pulpit) I can definitely recommend if you can find a way on.
Among the public options mentioned here, I can vouch for Lakeview, which is short and busy and won't wow with conditions but it's a classic and its greens are unique for an accessible municipal course. Osprey Valley's three courses are excellent and underused. Glen Abbey, sure, though the value proposition isn't great. Angus Glen, Copper Creek and Eagle's Nest are among the other big-name daily fee options.
Farther afield: Tarandowah is a low-cost farm links that is very good for low cost, an hour west of Oakville. Muskoka's high-end resort courses (including Bigwin, Taboo, Deerhurst, Rocky Crest, Grandview, Muskoka Bay, Ridge at Manitou and some lesser lights) are worthwhile in memorable topography if you can justify travelling a bit farther. Buried in Mark's list is Kawartha, an hour outside Toronto in Peterborough. It's a super Thompson layout with a recent Ian Andrew bunker redo that takes outside play -- you won't regret that trip. (Here was Mark's brief Kawartha tour for GCA:
http://www.golfclubatlas.com/forum/index.php/topic,50640.0.html)