Tax Depreciation, Modernization, and Simplification Act of 2007 - Amends the Internal Revenue Code to: (1) authorize the Secretary of the Treasury to modify or create new class lives for depreciable business assets that reasonably reflect anticipated useful life and decline in value; (2) eliminate the mid-quarter accounting convention for determining depreciation; (3) allow an election to consolidate, in a mass asset account, the accounting of depreciable properties that each cost less than $10,000; and (4) extend permanently the $100,000 expensing allowance for depreciable business assets.