But: If yours is a "personal service corporation"--meaning the corporation's main output is your own work effort, for instance as consultant or pet groomer--then all your profits are taxed at a flat 35% corporate rate and you'll usually do better with a passthrough.

FORBES: Investment Guide: Self-Employment

Taxpayers usually have a choice: Either deduct a flat 51 cents per business mile (in 2011), or write off IRS-approved depreciation plus actual costs for gas, maintenance and insurance, among other things.

WSJ: Tax Report: The New Tax Breaks for Business Autos

Around the fourth day of the illness, a rash - flat red or brown blotches - may appear, usually starting on the forehead and spreading downwards.

BBC: Q&A: Measles and MMR

In the music industry, a custom studio usually refers to a recording business, built small and charging cheap, designed for aspiring artists with big dreams but flat wallets.

NPR: 'Downriver Revival': Documenting The Double U