BNA Portfolios are housed here. If you're doing tax research, at some point, someone is going to point you to the BNA portfolios.
There's a lot more on Bloomberg Tax, including various calculators, calendars, and charts.
Hein Online is an online publisher much like Westlaw and Lexis. They excel in historical materials.
Tax Foundation Archive Publications
Tax Foundation Archive Publications: According to Hein, "[t]his collection provides convenient access to the complete archive of the Tax Foundation's publications from 1937 to date, which contain information on taxation, fiscal policy, finance and more."
The Tax Foundation describes itself as: "the nation’s leading independent tax policy 501(c)(3) nonprofit. Since 1937, our principled research, insightful analysis, and engaged experts have informed smarter tax policy at the federal, state, and global levels. For over 80 years, our goal has remained the same: to improve lives through tax policies that lead to greater economic growth and opportunity."
These materials are excellent for tax scholars and researchers. If you're working on a niche subject, this is well-worth a look.
Some of their archived materials on Hein include things like:
Taxation & Economic Reform in America Parts I & II
This is a great source of historical information. Hein describes it as: "HeinOnline’s Taxation & Economic Reform in America brings more than 300 years of legislation to your fingertips. Containing more than 20,700 volumes and 4.8 million pages, this database allows researchers to search across tax regulations, laws, and hundreds of legislative histories dating back to 1700. Also included is the complete Carlton Fox Collection which contains nearly 42 years of historical legislation related to the internal revenue laws from 1909-1950."
Standard Federal Tax Reporter (1917-1985) "This database contains a comprehensive collection of federal income tax information, such as the full text of all proposed, temporary and final federal income tax law regulations, as well as full text of federal administrative rulings and documents. HeinOnline coverage is from inception through 1985."
Some of the big treatises on Lexis include:
UST's LibrarySearch is great. GREAT, I tell you. Besides searching UST materials, it also has the capability to search surrounding libraries. It also searches both print AND electronic resources.
If you click on a resource below, check out the right-hand side of the page! The suggested other materials list is great. (GREAT.)
Some Resources Available:
This is another big secondary source you'll likely hear mentioned. While UST doesn't have a subscription, you can register for a free trial on its website if you're in a pinch.
Westlaw has some of the heavy hitters in tax secondary sources: