This is propably the best website I've found for plotting biking and running routes. Plotaroute.com
. You can simply plan your own route, or let it do it for you and is particularly good if you want to plan a pre-determined distance. You can then save (with a login) or download the route to load onto your favourite GPS device.
The auto-planner is not so good for XC routes, which is where the self-planning comes in nicely. I used to use Bikemap.net, but this is far superior I reckon.
(There was an old thread on this, but I couldn't find it; if a Mod can locate it, feel free to merge)