From Forbes.com: The 10 Most Profitable Businesses To Start
No. 1: Accounting Services
Average Pretax Margin: 25%
This industry includes services like bookkeeping, designing accounting systems, payroll billing and preparing financial statements and tax returns. A big yawn--until you see the profits start to pile up. Three reasons: pricing power (everybody needs accountants, no matter how the economy is doing), low overhead and marketing scale, thanks to plenty of repeat clients.