Pavane is right about Pictish names in Scotland, they are mostly to be found between Aberdeen and the Firth of Forth. Mostly they are combination names, with a Pictish generic (like 'hill' or 'field') and a Gaelic specific (like (hill) 'of the fox', or 'of the smith'). As I remember most of them are Pit- names, like Pittenweem. Pit is supposed to mean 'portion of land' or something vague like that.

And Scabby Doug has the Falkirk thing right too - the pre-Scots name is spelt Eaglais Bhreac and it's Gaelic. It's a nice example of successive incomers translating the existing place name. There are lots of Gaelic names all over the lowlands of Scotland, which most people seem to find surprising. For example near Edinburgh you find Auchendinny (Achadh an t-sionnaich, 'Field of the fox'), Ballencrieff (Baile nan Craoibhe, 'Tree farmstead'), Gullane (Gualainn, 'shoulder' of land). And conversely most of the place names in the Western Isles, perceived heartland of Gaelic, are of Norse origin...

In England a lot of the major towns and cities have pre-English names... Carlisle, York, London spring to mind immediately.

Will stop yadding on now... could go on for hours about placenames :-)