This guide focuses on sources of financial data for research purposes. Sources are divided by type and often further subdivided. Most financial databases are restricted to academic use only for Princeton University.
A few tips for finance:
Tickers can be reused. Ideally, find the CUSIP, ISIN, and/or SEDOL. Often, you will need to spend time matching data from differing sources that use different identifiers and conventions.
Be aware of survivor bias. Some databases only include actively traded companies.
Be aware of "header" data, i.e., current-only addresses, industries.
You will have much less information for private companies than public.