Small Business Expensing Permanency Act of 2006 - Amends the Internal Revenue Code to: (1) increase and make permanent the taxpayer election to expense (i.e., deduct all costs in current taxable year) depreciable business property, including computer software; (2) increase the investment threshold amount used to calculate reductions in the amount of such expensing allowance; (3) allow an inflation adjustment to the amount of the expensing allowance and the investment threshold amount; and (4) make permanent the taxpayer's right to revoke an election to expense.