Dealextreme are selling Dualshock 3 clones for £18.60 each.
I personally have tested these and can say that there is no real difference between these and the genuine article. (Though some reviewers report harder to control analog sticks)
Also has a larger battery than the genuine ones, so you might want these over them anyway!
They are now compatible with ALL firmwares after sony locked the old ones out with 3.00.
With the cheapest genuine dualshock around £25 you stand to make at least £7 saving.