Equasis: Free registration available to http://www.equasis.org/EquasisWeb/public/HomePage
This gives you easy access to reports on Vessels (who the registered owner, beneficial owner and operator is). You can also pull a .pdf report on a shipping company which will include the vessels they own.
Seaweb: (Subscription)
Similar information to Equasis but has much more search and exporting functionality. Gives you reports on vessels, and also shipowners including their fleet information, latest press and basic company information. Also has ship Movements and News modules.
LLoyd's List Intelligence (Subscription)
This tool does all of what Equasis does plus a lot more. It enables you to add more complex filters to find vessels, set up alerts to track vessels, search on previous names etc. There is also more information on the movement of the vessel, generally and also via AIS (Satellite).
Bloomberg
The Bloomberg terminal has a BMAP command - then choose Vessels & Ports from the menu. You can get some quite good maps of where the vessel is currently located as well as the last few months movement data. The AHOY menu gives details of commodities trade flows, destination, origin, charterer.
Clarksons: (subscription)
Clarksons has a number of tools including World Fleet Monitor and Shipping Intelligence Network which give you information on vessels and shipowners as well as allowing you to collate information on top owners in countries or jurisdictions. It also has excellent data on the shipping market generally with weekly, and quarterly reviews and outlook reports on the world fleet, trade, shipping industries, rates and markets.
Marine Traffic https://www.marinetraffic.com
Free basic information such as the current location of a vessel but detailed options such as historical tracks are on a subscription basis.
Much of this is dealt with by international conventions. Searching for these on the Treaties section will give you a good indication of who has signed up, but for example the Protocol to amend the International Convention for the Unification of Certain Rules of Law relating to Bills of Lading signed at Brussels on 25 August 1924 (the “Hague-Visby Rules”) has equivalents in domestic law that may not be obvious. It is therefore good to check the Ratification of Maritime Conventions which is on i-law and this seems to bring in domestic implementation of the conventions have implemented in domestic legislation: e.g. t says “India’s Carriage of Goods by Sea Act includes provisions similar to the Hague Rules"
A good proportion of the news is not available on the consolidated services like Nexis. The key tools in shipping news are Tradewinds, Fairplay (from IHS Maritime) and LLoyds List.