It's a rare day when I don't find myself using this site at some point. Though it has a useful basic map function, the site's route planner is its key selling point. Mainly covering Europe and the US, though its range of countries is expanding, you can type in your starting point and end destination and it will plot a recommended route from door to door, tell you roughly how long it should take and what the petrol costs are likely to be. You can also choose to plot a route by bike, on foot or by speed, economy or sightseeing opportunities.
Like that? Try www.rac.co.uk; www.theaa.com