Wikipedia. Most of its entries include useful bibliographies, so Wikipedia can be a good place to get your bearings about a subject and to find and jump into additional resources.
Take books, for example. Wikipedia contributors are asked to add the sources of their information to article bibliographies, and if those sources are books, they'll include a hot-linked ISBN.
If a particular book listed in Wikipedia is of interest to you, click on the ISBN. You'll be taken to another Wikipedia page called "Book Sources" (and if you don't scroll down, you'll think 'big deal'). This page, however, is set up to help you find physical copies of the book. Scroll down to the online databases section. Worldcat is the first listed option. Click on "Find this book" on the WorldCat line, and an automatic search will be run on the book's ISBN in the WorldCat database. You'll immediately see if it's available at Plough Library. If it isn't, WorldCat will show you other libraries with the book.