Wolfhounds are gorgeous and used to be on mine and dh's 'must have one day list'. We had the most gorgeous golden one come and swim with our dogs in the sea in Ireland one year and were absolutely smitten, but having lost a dog to cancer aged 7 years, the life expectancy would seriously put us off. We do have a luvverly 10 year old Deerhound/Saluki x Greyhound (or possibly Whippet)/Collie though and he is just the sweetest, gentlest lump of love. 
SmartAlec Azawakh's are stunning, but I'm told very, er ... interesting to look after. Same with Sloughis that were also on my must have list, until I chatted with an owner one day.
Dh and I both dream about having an enormous old style GSD like our very first dog (rescued her aged 7) again one day, but understand that it's extremely unlikely we could ever find one like our old girl.
We both love Leonbergers and Bernese Mountain Dogs, but again, it's the life expectancy thing.
I think our next dog will most likely be a Whippet or Whippet Lurcher, as we'll need a dog that can keep up with Pip. I'd love a Beddie/Whippet, but having known quite a few am not sure I'm man enough for the challenge. 
I do love naughty terriers, particularly Parsons JRTs, but don't think we have the right environment for one where we are now (noise sensitive attached neighbours). My Aunt has two and they're completely bonkers but so unbelievably cute. 