Forms.gov
http://www.fedforms.gov/
The U.S. Government's home for all types of Federal forms from the various Federal agencies.  Provides a search box to search for a form by agency or alphabetically by form name. You may also browse frequently used forms by catagory - Tax Forms, Small Business Forms, Social Security Forms, Veterans Benefits Forms, and FEMA Forms.

Tax Forms/Information for all 50 States

Selected Tax Information Sites

1040.com
http://www.1040.com
Provided by Drake Enterprises, LTD this site has up-to-date tax news and tax information for everyone as well as links to federal and state tax forms, addresses and telephone numbers.

AICPA Online
http://www.aicpa.org/index.htm
"With more than 330,000 members, the AICPA is the premier national professional association for CPAs in the United States."  Site includes tax topics.

Federation of Tax Administrators (FTA)
http://www.taxadmin.org/fta/rate/tax_stru.html
Site summarizing state tax structures in a series of tables including state individual tax rates,corporate tax rates, sales taxes, and cigarette, distilled spirits, wine and beer excise tax rates.

Internal Revenue Service
http://www.irs.gov/
The home page of the IRS provides information about and resources for e-filing along with Frequently Asked Questions and Tax Stats..

Multistate Tax Commission
http://www.mtc.gov/
This organization of state governments exists to work "with taxpayers to administer, equitably and efficiently, tax laws that apply to multistate and multinational enterprises".  Provides a clickable map under Member States to visit tax sites of the 50 states.