[One of these made me think of the other ...]
From the Quotation of the day mailing list, 2011-11-30:
"There is only one party in the United States, the Property Party... and it has two right wings: Republican and Democrat. Republicans are a bit stupider, more rigid, more doctrinaire in their laissez-faire capitalism than the Democrats, who are cuter, prettier, a bit more corrupt - until recently - and more willing than the Republicans to make small adjustments when the poor, the black, the anti-imperialists get out of hand. But, essentially, there is no difference between the two parties." -- Gore Vidal, from Matters of Fact and of Fiction.
(submitted to the mailing list by Mike Krawchuk)
"It's like, duh. Just when you thought there wasn't a dime's worth of difference between the two parties, the Republicans go and prove you're wrong." -- Molly Ivins (via Jone Johnson Lewis' collection of quotations on about.com)
[I think Vidal has a good (important) point, but I'm going to ultimately have to side with Ivins.]