Didn't get a new bike under the tree this year? Try searching for one on an online classified such as Craig's List or Kijiji.
Kijiji, which is a little prettier to use, is a great resource to find a used bike. While Peterborough doesn't seem to have caught on to Craig's List, Kijiji is quite heavily used and there are quite a few Peterborough Bike listings. It doesn't take too long to fall behind the GTA Bike listings as there are a few bikes listed every hour.
One frustrating aspect for neighbouring cities such as Bowmanville, Lindsay or Cobourg is that neither buy & sell lists you.
Currently, I have the Peterborough Kijiji feed running in the sidebar.