About two years ago, I described the process of creating a list of caches along a particular route. At that time, you had to create the route in Google Earth, save the file, and then upload it into geocaching.com as the first step in creating a pocket query of caches along a route.
Over time, the process has gotten much simpler, and can all be done without leaving the geocaching.com web site. For detailed instructions, visit this link. Or, you can just dive right in by clicking on the "Create a Route" link from your gc.com Profile page. That will take you to the Create/Edit a Route page at http://www.geocaching.com/my/routeedit.aspx. From there, just enter your begin and end points, and the search radius, and click "search". You'll then see a map displaying the entered information, which you can save by clicking, "Save Route Changes".
From there, you can save it for public consumption, or keep it in your private directory of routes. You can also download a GPX file of your route, which you can send to your GPS receiver as a route file. At this point, you also have the option to create a pocket query along your newly created route. This option will generate a new pocket query containing all the caches along your route within the search radius you provided.
And that's all there is to it. Cache On!