The Internal Revenue Service (IRS) 
Downloadable tax forms and publications as well as a lot of great tax advice.

Illinois Department of Revenue
 
Bartlett Chamber of Commerce
The Bartlett Chamber of Commerce provides programs and services for members to meet new customers, develop effective partnerships, increase profitability, improve professional skills, and promote business interests in government affairs. 

Electronic Federal Tax Payment System
The easiest way to pay Federal taxes.

AICPA
The American Institute of Certified Public Accountants and its predecessors who have been serving the accounting profession since 1887.