AA Route Planner: The AA Route Planner is probably the most popular online route planner in the UK. Plan your car journey, include waypoint, points of interest and other useful advanced features
Bing Journey Planner: UK and European Routeplanner and road map provider
Britannia Rescue: Plan your point to point journey, UK, Ireland and Europe. Also allows via waypoints and shows journey distance, time and fuel consumption. Routeplanner is at the bottom of the homepage.
Google Route Planner: Google Maps also offers directions. Plot your point on Google maps and then get direction to or from this point to or from another. The Google Route Planner is extremely effective and covers the whole world and you can easily switch between different modes of transport for journey times and directions.
Greenflag Routeplanner: European and UK route planner from Greenflag
Holiday Autos UK Rounte Planner: Simple to use basci route planner. Select UK from the dropdown then add your to and from addresses.
Map24.co.uk: Map 24 also provide a UK and Europe routeplanner and roadmap for drivers
RAC Route planner: The RAC provide this route planner which covers the uk and europe too.
Tom Tom Route Planner: The Tom Tom Route Planner uses some clever geolocation to drop you into a map of the area you are located. It isn't foolproof of course but it can be quite accurate. The map shows any traffic hotspots in your area. You can set your home location or your journey's start and finish points by right clicking any point on the map.
ViaMichelin.com: Pan-european road journey planner from Michelin