Government and Political Sites:
IRS Calendar - for small businesses and self-employed
Social Security Administration
Small Business Administration
Internal Revenue Service - for tax forms and instructions
Official site for U.S. government information
US Congress on the Internet - legislative information
Vote smart - political topics plus status of current legislation

Reference Material and Lookup Sites:
Total Tax Insights Calculator - estimate your total federal, state, and other taxes paid
360 Degrees of Taxes
College Financial Aid Helper
Section 529 College Savings Plans
Choose to Save  - savings tips and a great retirement calculator
MapQuest
Currency converter - any country to any other country
Zip code lookup - use any address
Business yellow pages - by state, by name
Webster's - dictionary and a thesaurus
Official US time by zones
Measurement converter - how many centimeters in an inch and numerous other conversions
Calculators - for almost any job under the sun
The ultimate reference desk - You can search the reference desk topics by keyword or table of contents.
Free Trip - how to get there
Peoplefinder
Record Retention Guide

Business Startup:
Wall Street Journal Startup Calculator
Sample Business Plans
Business Plan Starter 

General sites:
Ticketmaster - which events interest you?
Real estate listings - nationwide