The BGS have put up a nice interactive map of the UK’s geology (flash required). You can select and deselect rocks of different geological periods to see where they are distributed around Britain and Ireland, and if you hover over the information symbols it will show you their absolute ages and stratigraphic subdivisions.
It’s not as pretty as William Smith’s effort, but it’s a neat tool, and nicely summarises the larger-scale geological patterns such as the obvious increase in the age of the exposed rocks as you strike northwest from Dover (there’s a nice story behind that, which I need to get around to posting one day). The BGS also provides online access to higher resolution data, although the implementation is a bit more fiddly (you have to zoom in a bit before you can display basement geology, too).
(Via the Isles Project)