A Little Bit of Everything:
BadgerLink is a great resource meant for anybody who lives in Wisconsin. You have access to it if you have a library card with any public or academic library, which is free. You can find newspaper archives, books, magazines, and Spanish Language materials. You can also search by subject. The site is aimed at the general public, but has a large amount of valuable resources for research or cite-checking.
Google Books: http://books.google.com/
Google has digitized a wide variety of books on a wealth of subjects. To search for free e-books, first search for the item you want. Then simply narrow your search using the 'free google e-books' link on the left-hand side of the the screen.
Internet Archive: http://archive.org/
The Internet Archive has been digitized texts, music and old webpages for public use. If you are looking for books, use the search bar and the category 'texts'.
The HathiTrust is a collection of universities who are preserving their materials digitally. You must log in via the University of Wisconsin system in order to download any pdfs, but anybody can view the items online.
Directory of Open Access Journals: http://www.doaj.org/
You can search either by journal title or within articles using a keyword search. Journals that are open access allow all users to access their content free of charge.
Google Scholar: http://scholar.google.com/
Google Scholar gives you access to articles that have been uploaded to the internet by publishers or authors. If you search Google Scholar while logged in as a University of Wisconsin student, Google Scholar will connect you with our library catalog to access journals that are owned by Wisconsin as well.
Wikipedia List of Online Newspaper Archives: http://en.wikipedia.org/wiki/List_of_online_newspaper_archives
Wikipedia has compiled a list of Newspaper archives that are mostly free, but some cost to view articles. They are sorted by country, and list whether they are free or not next to each link. Very easy to navigate and a helpful link to remember.
Wisconsin Newspapers Digital Research Site: http://badgerlink.newsmemory.com/wna/badgerlink/
A site dedicated solely to Wisconsin newspapers. The papers are from 2005 to current, with a delay of 60 days. If you are looking for recent newspaper articles, this site may be a great resource for you. The papers are updated daily, so they are only two months behind.
Chronicling America: http://chroniclingamerica.loc.gov/
Run by the Library of Congress, this sites hosts thousands of papers that were published before 1922 (pre-copyright). If you are searching for historical legal cases or precendent, there is a good chance it can be located here.