Disband the IRS (Internal Revenue Service). Replace the IRS with a national sales tax.

Use existing state sales tax mechanisms to collect the taxes. Where no such taxes are collected, create the mechanism following existing state guidelines. The benefits of this change are numerous: collection of taxes is instantaneous, visitors to the U.S. pay into the system, cheating on taxes is removed, abuse by the IRS is eliminated, everyone pays their share, the mechanism to collect the taxes are already in place in most states...to name a few benefits.