I usually use gumtree and Ebay but there don't appear to be the bargains or volumes atm. Could be a seasonal thing or am I missing out on a hot new site
Carsandclassics, ebay, auto trader and sometimes gumtree. Sometimes I have a looksie at Car-transplants, they do some very cheap (lightly damaged) cars if that's your thing. UK-Repossessions is always fun to look at, some bargains as well.