I`ve always done well on www.boatsandoutboards.co.uk I sold my 1991 Fairline Phantom 41 on there and got top money for her (130K+). That was in 2003 mind you. You could try www.boatshop24.com as well.
Just sold our boat through MBY. Lots of enquiries, wonderfully easy sale, buyer viewed boat in the morning,no survey, transferred cash to our Bank same day afternoon, took it away two days later. Only problem - we haven't got a boat!What shall we do now?!