We went to one of those Tesco 'extras' yesterday and they had a huge range of wooden tracks. you know they type - the traditial wood tracks that fit loosely together and come with magnet connecting trains.
Brio make the original type but they're deadly expensive. Ikea make a really cheap little set but the range is limited but Tesco seem to do a huge range of different tracks (turnstyles, crossing, high speed locomotives and loads of little trees and mountains)... at Ikea prices if not cheaper. excellent value for money. for about £20 I can double up DS's set and completely cover the front room in wooden tracking (to DW's delight LOL!)