Laws made by the United States Congress, which is legislation that passes both the Senate and House of Representatives.
Each section of the U.S. Code on FindLaw contains a date, located in the upper right hand corner of the page, which will tell you the law enacted as of that date. To check if there have been any recent ammendments to the section you are looking at, you will need to check the U.S.House server's list of amendments, which includes changes to the U.S. Code from the 105th and 106th sessions of Congress. The list will give you a brief notation of what has specifically changed and a Public Law (a recently enacted law) number. Public Laws can be read in their entirety at the Library of Congress Thomas web site. Thomas includes the text of all versions of House and Senate bills and the Congressional Record (the "minutes" of Congressional hearings).