The whole of Halkidiki!!!! Hire a car or motorbike and get out and see the place...Sithonia, the other peninsular is beautiful, many nice beaches! Thessaloniki is also an amazing city!
Take a look at my site www.@#$%&.com for some pictures from around Halkidiki. There's more to this place than alot of people realise!
Cheers,
Nic!