The new Silver Snail location at Yonge and Dundas is a must if you're from out of town, and there's the big EB just down Yonge from there. In the Atrium, around there just to the north of the Eaton Centre, is Game Shack. They've generally got some good prices on retro stuff. If you're heading north past College I would check out One Million Comix and maybe Hairy Tarantula. On Spadina there's a bunch of stuff through Chinatown, all very obvious from the outside. The new A&C Games is at Spadina and College, but I haven't been since the move so I can't really vouch for it. There's a couple retro game places in Kensington, and north of there along College are a bunch of computer stores if you need some cheap parts.
That's some of the major points of interest. Sort of hard to narrow it down not knowing what you're looking for, what you're already familiar with and where you're going on those streets.
For comics, there's a bookstore called BMV west of Yonge and Spadina, the third floor is the comic book/graphic novel/manga floor. Across the street is the Labyrinth, which leans more towards art books, and further west past Bathurst is the Beguiling.
Suspect Video is nearby there too but I haven't been there in like over a decade, so I don't know what they're like now.
A&C Games used to be just south of Yonge and Spadina, but they moved even further south past College, it's a bit of a hassle to walk there from Yonge and Spadina especially in the winter. Even further south from there is AnimeXtreme, lots of figures and merch there. Even further south than that is Meeplemart, a store dedicated to board gaming, although they've got a figure section. Iceman Games has a store a little west of A&C, as well.
And if you're willing to head further east of Yonge and Spadina there's Game Centre which is close to Yonge and Bloor.
If you had a couple of tokens or a day pass, you'd be laughing.
Among what others have mentioned in this thread, you might hit up the Toronto-Age thread as well. OT has suggestions for what you're asking for, but others will have their own.
Thanks for the help guys. You've confirmed everything I've written down. I've planned out my walk/transit path, and you've mentioned all the places I'm hitting up.