These sources include sample forms and contracts on a wide variety of subjects. Many of these sources are also available in print in the Law Library.
You can find additional sources of forms by browsing Lexis Advance by category, then by forms.
EDGAR is the SEC's database of filings from publicly traded companies. It's available free from the SEC, and is also available (with perhaps easier interfaces) on commercial systems.
Bloomberg Law (in Dealmaker Documents) and Westlaw (in Sample Agreements) both draw from EDGAR filings—specifically contracts filed as Exhibit 10, Material Contracts. This gives researchers access to a variety of real-world contracts. The set of contracts found in EDGAR is very large, but it is limited:
From the SEC's EDGAR guide:
What types of “material contracts” must an issuer file as Exhibit 10 to a registration statement or periodic report?
How to get to EDGAR search:
In search template
Free website presents EDGAR material contracts and separate collection of clauses. It lacks the bells and whistles of the high-priced databases, but it's free!
How to get to EDGAR search: type edgar in search bar. Choose SEC EDGAR Filings, Combined.
Search tip: in template's Form box, enter exhibit 10.
How to get to EDGAR search: type edgar in the search bar. Choose EDGAR Filings & Disclosures. (Note you could also go to EDGAR Precedent Agreements - Clause Search.)
In search template: