This site isn't going to win any awards for style and it can be a little fiddly to use, but it's a triumph of function over form, and well worth persevering with. For journeys on public transport throughout the UK, it will help you plot a route from A to B, giving a variety of options and operators so you can compare journey times. A non-profit service funded by the UK Department for Transport, the Welsh Assembly Government and the Scottish Government, it also gives car-route options for those who want to compare public and private travel.
Like that? Try www.traveline.org.uk; www.sustrans.org.uk