Regulations are codified in the CFR §26.
Current Regulations
Westlaw's federal (AND STATE) tax regulations
Lexis' federal tax regulations
Bloomberg's federal tax regulations
IRS's own tax regulations
Abbreviations
CFR or C.F.R. = Code of Federal Regulations
Fed.Reg. = Federal Register
TD or T.D. = Treasury Decision
Treas.Reg. = Treasury Regulation
Citations
ALWD
Bluebook