Certainly some of the Trappist Tripels, Westmalle & Westvleteren are two that come to mind. I've had some great vintage examples of both. Another style would be the Golden Strongs. You say Duvel drops off really fast. In some side by sides with Duvel, a number of us prefered the 2-3 year old examples to the fresh.
< edit to add Blond beers >
(Blond ->Westmalle & Westvleteren I like fresh, the darker beers do get far better with age. The thing with Duvel was when we had delivered fresh that morning vs bottles a few weeks older. The fresher was bursting with hoppy aroma with a huge rocky head, while the slighty older was already fading. Nit picky but it really made a impression on how fast beer can change.
fresholderWhere in FL are you, Uthristy?
If you're interested in attending some tastings of vintage beers and are close enough to make a trip to Ocala, go ahead and pm me. Jim Ritchhart, one of our club members (of Gainesville's Hogtwon Brewers) lives in Ocala. He puts on vintage beer tastings on a semi-regular basis. I help him organize those. Let me know if you're interested.
Close enough that you may have drank some of my beers

But really my wife signed us up to Hogtwon Brewers several yrs ago but we never went, LOL
We're by Newberry & Trenton.
I've heard about Jim Ritchhart from
http://belgianbeerboard.com/, we also visit Belgium alot.
Our beer _ tour pics
http://s821.photobucket.com/home/UknowWho2u