In a 15 gallon, you could do a couple of small clowns, and a couple small gobies. I like yellow and green clown gobies, and the Catalina Goby is crazy colorful. Some inverts like Porcelin Crabs and Cleaner or Fire shrimp would be awesome as well.
Here is a link to Nano tank Fish:
http://www.liveaquaria.com/product/a....cfm?c=15+2124
Liveaquaria is a good place to search for ideas on livestock. They have a pretty decent database for lots if different fish/inverts/corals. (Just remember its just for information as they do not ship to Calgary).
As for subsrate, just do an inch-ish thick layer of Caribsea Agramax Select sand. A 30 lb bag of it should be sufficient, and you can pick it up at your local PetSmart for way cheaper than anywhere else.
Caribsea Aragamax Select Sand / Substrate - 30 lbs