...Check out Stock.Xchange.
Search for "bicycle" (without the quotes ) and you'll get pictures of bike races, classic (vintage) bicycles, up-close black&white shots of bike parts, and peaceful scenes of bike destinations.
It sounds like I'm selling the site, but I actually stumbled across it when I was looking for free photos for a website I was making.
Most of the photos have NO usage restrictions whatsoever... Use them on your website, in your store, on your computer, wherever.
The small previews are nice for avatars, etc. To get the full size image (often 1024x768 or 1600x1200!) you need to make a free account with them.
Some of my favorites (scaled down for the forums):