<p>Vassar's library.</p>
<p>I second Vassar.
Wesleyan's is also pretty nice.</p>
<p>In the "modern" category, I'd give it to NYU.</p>
<p>
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Brown's libraries (the "Rock" and Sci Li) definitely get my vote for the ugliest library exteriors.
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<p>Clearly you've never been to Brandeis. My alma mater takes a backseat to no school when it comes to hideous architecture.</p>
<p>I think that Columbia's Butler Library is particularly impressive (at least on the outside), especially at night.</p>
<p>There are many libraries on the campus at Univ. of Southern California, but for beauty I think the Mudd Hall Philosophy Library is a gem. Leading up to the library are a series of arches and beautiful landscaping. The building is often seen as a background in films.</p>