I answered the above question on Quora, but I thought it was worth posting the answer on my blog as well.

B2B is a broad category, so I will be providing a high-level process:

• Start with the open web — the company website, corporate blog, Facebook, Instagram, Twitter, LinkedIn, YouTube, Vimeo, and SlideShare.
• Jump to the LinkedIn and Twitter pages of key executives.
• Continue with third-party review sites such as TrustRadius, G2, Glass Door, and Quora. Also compare web (Alexa, SimilarWeb) and social media activity (Owler) of the company vs. its top competitors.
• If a US public company, obtain their 10-K, 10-Q, Annual Report, Proxy, and 8-Ks. Also, review all material on their investor page and look for Fair Disclosure Earnings Transcripts (Seeking Alpha, NASDAQ), investor presentations, financial models, etc.
• If a US or global public, analyst reports are often available subject to a one week embargo. Vendors with analyst reports include D&B Hoovers, Factiva, Zacks, FactSet, Capital IQ, and Investext. Reports with fewer than five pages tend to only look at the stock, and provide little in the way of detail. Particularly good are the Initiating Coverage reports as they often entail an overview of the business.
• If a US or global public, review the synopsis of material events going back over a decade. Significant Developments are available from Reuters, Factiva (Reuters), D&B Hoovers (Reuters), Capital IQ, and FactSet.
• If a European private, they are likely to have filed financials, directors, and shareholdings with a local registry. You can obtain these through D&B Hoovers, Bureau van Dijk Orbis, or local registries.
• Major companies are profiled by MarketLine and Global Data. Check to see if they or key competitors are profiled. Industry vendors also profile companies and products within their target segments.  These profiles include SWOTs, company histories, market shares, and overviews of key products and segments.
• Determine the firm’s list of competitors. If it is a public company they will list this in a proxy. If it is a private company, refer to Hoovers, Global Data, or Marketline.
• If you are looking for technology employed, refer to Datanyze, HG Insights, BuiltWith, DiscoverOrg, or RainKing. [DiscoverOrg, RainKing, and Datanyze have all been acquired by ZoomInfo]
• Review all news for the company. The open web thins out quickly, so you are best off using an archival service such as Factiva or LexisNexis
• For Intellectual Property and Legal, use LexisNexis or Westlaw. You can also search the USPTO site for trademarks and patents.
• Check research from industry vendors. Most focus on only one or a few sectors (e.g. Gartner, Forrester, and IDC for Hardware and Software). A few provide higher level market overviews at the country or global level which include national or regional market shares, forecasts, and mini-profiles of the top 3-4 competitors in the market:
  • MarketLine (country and global)
  • Euromonitor (country or global)
  • BMI (Emerging Markets)
  • Freedonia (US)
  • IBISWorld (US, China, Australia, Global)
• A few US industries are required to file with state or federal agencies. These include banks (FDIC), insurance (states), and nonprofits (990 forms with the IRS).
• Larger companies file ERISA forms (5500s) annually with the Department of Labor. This filing covers benefit plans so is useful for direct research on a company and plan advisors. Judy Diamond offers a freemium service (FreeErisa) for ERISA filings.
• If the firm has PE or VC funding, refer to Crunchbase, DataFox, Mattermark, PrivCo, or other vendors that collect this detail. Crunchbase and Owler provide this information for free.
• Setup news alerts on the company and competitor you are evaluating. This can be done via Owler, Contify, Demandbase Sales Cloud (FKA InsideView), D&B Hoovers, Factiva, and LexisNexis.
• Obtain a credit report (D&B, Experian, or local credit company if overseas)
• Research the company family tree and review major subsidiaries and recent acquisitions. Global Family Trees are available from D&B Hoovers, Bureau van Dijk, and InsideView (parents and subs only). Public companies also list their subsidiaries in their 10-K (Note 21).
• M&A research can be performed with Zephyr (Bureau van Dijk), Mattermark, FactSet, Capital IQ, and other vendors.

This is a quick overview for secondary research.  For primary research, reach out to customers, partners, and former employees.  They can be identified via Case Studies (generally fans so don’t be overly reliant on them), customer references on site, TrustRadius, G2 Crowd.  Former employees can be determined via LinkedIn.  Partners are generally listed on the company website.

One area that is particularly difficult to obtain is pricing data.  Some B2Bs are transparent while others publish virtually no details, particularly if they have complex product lines and pricing.  Don’t be surprised if you find little in this area beyond “Pricing begins in the five digits” for many vendors.  Pricing details may require primary research and this will provide data points, but not full price lists.

If you are performing regular competitive analysis work, consider joining SCIP (Strategic & Competitive Intelligence Professionals).

Feel free to add additional tips in the comments.