Rundle ruins for sure just north of the Saddledome:

Rundle Ruins by
alexcgy, on Flickr
While in the area hit up the old sandstone Victoria park school right next to the arriva condo tower. You can get a pretty cool shot with the old school and a modern glass tower rising up above it:

arriVa by
BigtimeYYC, on Flickr
Across 11th avenue from it is the Biscuit block building, 4 storey red brick with a new modern addition on top.
Also check out the Alberta Ballet building by St. Mary's Cathedral in Mission. A nice long stone wall and wooden boardwalk if I recall. We did some shots there for ours.