The Athabasca Glacier is amazing, and amazingly accessible. Just inside the Jasper National Park boundary north of Banff, take Hwy 93 until you reach this natural wonder.
What's perhaps most amazing about the Athabasca Glacier is how accessible it is. You can simply pull into a parking lot, and hike up in about 10-15 minutes to the foot of the glacier. Make note of the many signs warning you to stick to the marked pathways - Many people have been killed by taking a wrong step and falling into a hidden crevace.
That being said, you can also hire a certified guide who can take you for an 'ice-walk' further up on the glacier. It's a very educational and interesting experience to be able to see such a remarkable piece of nature.
The Athabasca Glacier visitor center is also very helpful. They can arrange 'ice-walks' and provide detailed history and information about the history of the glacier. Make note of the dated signs on the pathway between the visitor center and the glacier. Every so often you'll see a sign with a year such as 1990 or 1950 which marks where the foot of the glacier was then. The glacier is currenty receeding as part of it's natural process and will only grow again during another ice age.
A visit to the glacier will leave a long lasting impression on you. The spectacular scenery of the drive alone is worth the trip!