There are some great rides around here. I wouldn't go up towards Sundre as above - roads are not great and the traffic is heavy. I rode from Calgary to Jasper and back this summer and we went up that route on the way to Edson. The ride back from Jasper down the Parkway was stunning, but obviously that's not too directly accessible from Calgary. Jasper to SK Crossing is the single best day I've ever had road biking.
If you are looking for a century, there is a nice ride starting from Westhills. Basically, you leave from Westhills, ride to Bragg, Bragg to Priddis, south to Millarville, and back around to Bragg via Elbow Falls. Check out the map (along with a lot of others of various distances) on this site:
http://www.albertarandonneurs.com/maps.htm