Smithsonian Open Access
Treasure trove of public domain scans of art and literature steeped in history.
APA Formatting and Style Guide (7th Edition) - Purdue OWL® - Purdue University
My professor is very intense about citing APA and recommended this site as our one-stop shop for a proper bibliography.
Rare Book School
Straight from my Rare Books professor at UIUC, these classes make a difference towards additional niche knowledge
Mendeley | Homepage
The way Mendeley works with MS Word is beautiful.