I am looking for sources of available datasets on M&A. My preference would be for a clean panel dataset that might have previously been used for the purpose of studying the effect of M&A on either firm profits, or their R&D activity. I know that this is rather specific, but any broader suggestions on good sources for M&A data would also be appreciated.
The effects of mergers: an international comparison (Gugler, Mueller, Yurtoglu, Zulehner) indicates that its "principal source of data" is the Global Mergers and Acquisitions database of Thompson (sic) Financial Securities Data (TFSD). Their "data description" (section 4) doesn't describe substantial follow-on work.
Starting from that reference, it appears that the Thomson database is the most highly regarded. (See "Sources for M&A Information" from the University of Chicago library. U of C library also refers to MergerMarket, which has free league table "data" (in PDF form) from 2011 on their site. The PDFs are computer generated, so would probably lend themselves to data extraction with a tool like Tabula.
Other papers I found described their methodology as something which sounded more labor-intensive, but perhaps if you contact authors, you might get more information about what they did and if they'll share it.
A competition at http://algomost.com/en/tasks/predict-acquisition contains the data on 2500 companies over 21 years and their M&A deals.
There are three basic sources of time-series data on mergers and acquisitions for the postwar period: the U.S. Federal Trade Commission (FTC), the periodical Mergers & Acquisitions, and the annual reports of W.T. Grimm & Co.