I'm no expert on mountain biking, but I do feel very lucky to have some great riding so close to home. Our local spot is Fish Creek, about 7 minutes' ride from our house. This area has been undergoing changes as biking has made the change from illegal to merely tolerated and controlled. Not exactly perfect, but it is nice to not be considered a criminal whenever you turn off the tarmac! Although some trails have been closed as a result of the negotiations, what's left and what's been created by the Calgary Mountain Bike Alliance is pretty darn good. If this urban park was in Britain, it'd be an area of national acclaim - and no doubt full of broken bottles and scary yoofs. 
Fish Creek is a great place to ride, and I never seem to run out of trails to follow. A second area that's dead popular with Calgary MTB fans is Bowness Park, home to numerous pleasant trails that thread alongside the river, including the slightly infamous Sideshow Bob (below). It's a nice area to ride in, with views of the mountains, and the Bow River running through, although for my money Fish Creek beats it.
