Toronto to BC and Back again. Hints on Yellowstone area?

I second the recommendation for the Beartooth Highway out the northeast entrance of Yellowstone. Within Yellowstone, don't miss these things:

Canyon area (Lower Falls)
Lamar Valley
Hayden Valley
Norris Geyser Basin
Old Faithful area
Grand Prismatic Spring and other hot springs pools

Also, you'll be really close to Grand Teton National Park, which is worth the short trip to the south if you're not already sick of looking at beautiful mountain ranges.