To take TBN's tip from the specific to the general:
Belgian Tripels (indeed, many Belgian high gravity beers), Barleywines, Russian Imperial Stouts, most Sours and generally big flavoured, high alcohol beers. The big exception is India Pale Ales of most sorts, which start to lose hops past the 3 month mark.
I've had great results with Guinness FES, which is too cheap not to try...