US Code. Mounted on the U.S. House Web pages contains links for a search engine and downloadable files for specific titles. 

Code of Federal Regulations.

Federal Register.

Findlaw. State resources indexes.

Municipal Codes Online .

ADA Home Page. Department of Justice Americans with Disabilities Act ADA Homepage.
 
ADA Design Guide 1 - Restriping Parking Lots. A 2-page illustrated design guide explaining the number of accessible parking spaces that are required and the restriping requirements for accessible parking spaces for cars and van-accessible parking spaces.

Common ADA Errors and Omissions in New Construction and Alterations. This 13-page document lists a sampling of common accessibility errors or omissions that have been identified through the Department of Justice's ongoing enforcement efforts. The significance of the errors is discussed and references are provided to the requirements of the ADA Standards for Accessible Design.

Accessible Stadiums. A 4-page publication highlighting features that must be accessible in new stadiums and providing guidance on line of sight for wheelchair seating locations.

Checklist for Readily Achievable Barrier Removal
 

The Architectural and Transportation Barriers Compliance Board, also known as the U.S. Access Board. The Board, created in 1973, has served the nation as the only independent federal agency whose primary mission is accessibility for people with disabilities.
 
Accessibility Guidelines for Buildings and Facilities 

Enviromental laws and regulations for protecting the environment.

Major environmental laws

Compilation of Selected Laws Concerning National Forests & Related Matters

Linklaw for laws, regulations, standards, and conventions related to cultural resources check out the National Park Services page which provides links to full text documents including material from the Code of Federal Regulations and the United States Code. 
 
The Secretary of the Interior's Standards for the Treatment of Historic Properties (36 CFR 68), which provides standards on preservation, rehabilitation, restoration and reconstruction of properties

Guidelines for Federal Agency Responsibilities, Under Section 110 of the National Historic Preservation Act sets out the broad historic preservation responsibilities of Federal agencies and intends to ensure that historic preservation is fully integrated into the ongoing programs of all Federal agencies.