Study aids of can be a great resource to fill in the back ground knowledge you lack on subject so that you can find a topic and write the paper. They are generally, not what you want to cite in you paper though. I recommend two:
West Academic Nutshells and Hornbooks can be found at the library's databases' page at http://umkclaw.link/db. You will need to sign onto WestAcademic with your SSO. You can also register and create a password so that you can take notes and highlight materials in the database.
Many treatises and Looseleafs (a set of notebooks that are updated regularly) are available to law students and faculty on the major services of Lexis+, Westlaw Edge and Bloomberg. Lexis+ is particularly strong because it ownes the Matthew Bender and MoBar CLE publications. Below is screenshot of the "Sources" page in Lexis+ but filtered for "Mathew Bender."
You can get to Treatises and Looseleafs through a variety of different ways besides the "Sources" tab on the Lexis+ splash page. Ask a librarian for assistance. You can use chat with us during normal business hours, email us at email@example.com, or call 816-235-1650. Below are just two examples from Lexis+.
Below are two examples of treatises and looseleafs available on Lexis+.
Of course, Weslaw also has treatises listed in its secondary materials. Bloomberg Law has "portfolios" and is particularly strong in tax materials, and is a favorite of practicitioners. It also covers banking practice, corporate practice, securities, health law, and privacy and data security (to find: Splash Page > Browse (uper left corner) > Browse Secondary Sources > Browse BNA Porfolios).
For background general encyclopedias are good for building background on basic legal concepts. The following are useful tools: