As mentioned in other answers, one reason the colonies broke from England was taxation without representation. As a U.S. citizen, you have representation by your elected Congressmen and Senators.
Article 1, Section 8 of the Constitution states, in part, "The Congress shall have Power To lay and collect Taxes,..." In Article 1, Section 9, it states, "No Capitation, or other direct, Tax shall be laid, unless in Proportion to the Census or enumeration herein before directed to be taken." Some people believe that income taxes are direct taxes, however, in a Constitutional sense, income taxes are INDIRECT. I could go into a rather lengthy explanation as to why this is, but instead I'll refer to a history of income taxes in the U.S. and a couple of Supreme Court cases.
The first income tax law in the U.S. was enacted in 1861 and lasted for 11 years. In HYLTON v. U S, 3 Dall. 171 (1795), Supreme Court Justice Chase, (a member of Constitutional Convention and presumably would know what the Constitution intent was) stated, "that he was inclined to think that the direct taxes contemplated by the Constitution were only two,-a capitation tax and a tax on land." In SPRINGER v. U S, 102 U.S. 586 (1880), where the court upheld a tax upon the income of an individual, the court stated, "Our conclusions are, that direct taxes, within the meaning of the Constitution, are only capitation taxes, as expressed in that instrument, and taxes on real estate; and that the tax of which the plaintiff in error complains is within the category of an excise or duty."
In STANTON v. BALTIC MINING CO, 240 U.S. 103 (1916), the court stated, "by the previous ruling it was settled that the provisions of the 16th Amendment conferred no new power of taxation, but simply prohibited the previous complete and plenary power of income taxation possessed by Congress from the beginning from being taken out of the category of indirect taxation to which it inherently belonged..."
The 16th amendment to the Constitution which states, "The Congress shall have power to lay and collect taxes on incomes, from whatever source derived, without apportionment among the several States, and without regard to any census or enumeration." was properly ratified. The entire reason for the amendment was to clarify the power to Congress to collect an income tax. It wasn't steamrolled through either. Congress passed the amendment in 1909 and the states took close to 4 years to ratify it. Whether the Secretary of State made any errors in declaring it ratified is now a moot point. The 16th amendment is part of the Constitution and it will take another Constitutional amendment to repeal it.
Now, for the law. The law is codified as Title 26 of the U.S. Code. It is long, complicated and boring, but you can read it at http://www4.law.cornell.edu/uscode/26/ or at http://www.access.gpo.gov/uscode/title26/title26.html For the actual text of the laws passed by Congress, you can read them in the U.S. Statutes at large. To the best of my knowledge, these are not available online. However, you can read them at most Federal Depository Libraries. http://www.gpoaccess.gov/libraries.html