Specialized tax resources are hybrids that include analysis and annotations by tax practitioners and experts, as well as the text of key primary sources (the Internal Revenue Code and Treasury Regulations). These resources are often the best place to start your research because they compile so much relevant primary and secondary material in one place. Think of it as one-stop shopping.
The Federal Tax Coordinator, 2d and the United States Tax Reporter are two useful specialized tax resources from the Research Institute of America (RIA). You'll find them on Westlaw and on Checkpoint
["Colorful Shopping Carts" photo by Jim, flickr code poet, license: CC BY-SA 2.0]
The BNA Tax Portfolios provide in-depth analysis on specific tax issues in a practice-oriented manner. Access them on on Bloomberg Law.
Lexis IRC (Internal Revenue Code) Explanations provide explanations drafted by Matthew Bender / Lexis editorial staff. These explanations are available on both Lexis+ and Lexis Tax.
You can find the recognized and authoritative Warren Gorham & Lamont (WG&L) treatises on both Westlaw and Checkpoint. These treatises provide expert analysis on major tax issues. Here are some selected titles. (This is not an exhaustive list.)
Below are two tax books written by USF Professors. The Law of Federal Income Taxation by Professors Joshua D. Rosenberg and Dominic L. Daher, provides expert analysis on major issues in federal taxation. Selected Federal Taxation compiles major tax statutes and regulations, selected and edited by Professor Daniel J. Lanthrope.
The Law of Federal Income Taxation by 
Selected Federal Taxation by