Driving, Dublin - Belfast

I'm driving from Dublin to Belfast next week and I was wondering if anyone could suggest a "scenic" route. I'm not looking to be in the car for 10 hours - but, I wouldn't mind going off the major roads a bit. I would love to see a good part of the coast line.
Any suggestions would be great! Thanks!

I would say that the most interesting coast that you could divert to would be in County Down, once you cross the border into Northern Ireland. Seeing some of that would involve leaving the main route at Newry. The Mourne Mountains, for example are well worth seeing, as well as Dundrum Bay and up the coast towards Downpatrick and Strangford Lough. You can leave the coastal route and head towards Belfast with ease when you have had enough of a 'detour'.