I noticed today that Google maps has added a "re-route" feature. All you need to do is hover your mouse over the blue route and it shows you a "holder" icon. You can drag this around neighbouring roads and google maps re-routes accordingly.
Your re-route is actually done by adding intermediate stop point, which has been possible for quite sometime now, but this just makes it easier.See screen shot (click to see a bigger view).
On the same topic, for those of us who live in the UK. You should check out the new updated Multimaps.com. Multi maps remains one of the most popular mapping tool out here in the UK. Admitted that it's new interface is nowhere as smooth or advanced like Google maps, but it still offers a whole bunch of local features like the nearest cash-point, railway stations and even wi-fi spots. Whats more, its maps are far more accurate than Google maps (my home and several other places are still shown a bit off on gmaps).
My favourite feature is that it gives you walking directions. After all, I don't take a car into places like London. Here's an example.