One of the best and most consistent Barrel Aged beers is Goose Island's Bourbon County Stout. They use Heaven Hill barrels for this. They do a good job with it and it cellars wonderfully. They have a very limited release coming out this winter that has been in a Pappy 23 barrel.

Being from CO, I'm partial to Great Divide's barrel aged Yeti and Hibernation. They use Stranahan's barrels. I think the young barrel definitely impacts the taste. Also, our desert like humidity is not ideal for barrel aging. I think the yeti goes in the barrel around 10% and comes out 9 months later at 12%. I don't think they do any secondary fermentation in the barrel. Most of that is evaporation.

Other good BA beers are:

Kuhnhenn barrel aged barley wine
Founders Kentucky Breakfast Stout
Deschutes Mirror Mirror barleywine
Hoppin Frog BA Boris stout
Boulevard Bourbon Barrel Quad
Anything from a Barrel from The Bruery
Lost Abbey Bourbon Angel's Share (the brandy version is not very good)
Port Older Viscosity

The only negative thing about the barrel aged beers is they are tough to find. They typically come out once a year in limited quantities. They usually don't get distributed very far from the breweries. I always grab a handful of them when I see them.