(1) http://voteview.com/ [source of original data; processed version distributed with permission of collators of original data]
(2) "Party polarization in Congress: a network science approach," A. Waugh, L. Pei, J. H. Fowler, P. J. Mucha and M. A. Porter, arXiv:0907.3509. [paper to cite for our processed version of the Voteview data]
Newly reprocessed data:
Raw data taken from voteview (voteview.tar.gz or 1-108, and get final 109 and 110 from voteview site).