If the #1 thing to do when you are at Moraine Lake is to go up the Rockpile Trail, then the #2 thing to do is rent a canoe. Like the Rockpile renting a canoe will give you another unique viewpoint of being on Moraine Lake. For those that can afford the once in a life time adventure of renting a canoe, by all means do so.
The canoe's are run by the Moraine Lake Lodge (9:30 - 5:00), you can check thier pricing information here.
An easy 1 minute walk around the side of the main part of the Moraine Lake Lodge, you'll see it as you come into the lake. If there are no canoe's available you can ask how long, but you will have to wait in line for one. So, if you are there on a weekend or you're planning to spend all day at Moraine Lake then come back a little later. If you're only staying an hour or so, best to climb the Rockpile Trail (20 min.) or walk the Lake Trail (1 hour).
A nice break from the hustle and bustle of the Moraine Lake parking lot or the Rockpile. On a nice day you can see clear through to the bottom of the lake.
YouTube Video of people canoeing around Moraine Lake.