An interesting independent website called Traces of History provides an overview of the Nazi-sympathizing activities of the German-American Bund.
The excellent History Matters site, from George Mason University's Center for History and New Media, hosts an good sample of Charles Coughlin's sonorous—if sometimes disturbing—radio commentary.
The Virtual Museum of the City of San Francisco hosts a small online exhibit devoted to Upton Sinclair's EPIC candidacy for governor of California in 1934. The site includes primary sources representing opinions both for and against Sinclair's radical communitarian vision.
The Long Legacy Project has produced a website devoted to "The Man, His Mission, and His Legacy." You won't find much material critical of "The Kingfish" here, but you'll find no better online repository of Huey Long content elsewhere.