The ugliest building in Ann Arbor is the Federal Building at the corner of Fourth Ave and Liberty. The Feds tore down a beautiful Masonic temple to put up this windowless monstrosity. It's bad enough that this building is ugly, but it's also dysfunctional. For example, the post office has no working vending machines, and there isn't even a mailbox accessible from the outside after hours.
Views from the west and northwest.
There is some excellent background by local historian Wystan Stevens in the comments to this Flickr photo:
Photo by Phil Dokas
A few of the buildings that were demolished so this hideous travesty could be built. These photos by Clan Crawford Jr.