In reply to Gaston Rubberpants: Last year I sold a mountain bike and a roadbike, both in excellent condition, both for over 400 quid. I advertised them here and on bikeradar and on another bike forum, cannot remember the name, and on gumtree. In the end both buyers were from gumtree....although with gumtree you've got to sit through the endless emails of the "send photo's I a bit skint u take 50 kwid?" variety - no name, no sensible offer, simply demanding photos not asking for photos, illiterate etc. I was a bit puzzled about receiving no offers from bikeradar - though one person emailed saying he saw the advert and someone commented it was dodgy as I was a new forum member trying to sell a mint condition bike.
Go Gumtree.