IRS:  www.irs.gov

Maryland

Maryland State Department of Assessments & Taxation:  www.dat.state.md.us/
Comptroller of Maryland:  www.comp.state.md.us/

Virginia

Virginia Department of Taxation:  www.tax.virginia.gov/

District of Columbia

Office of Tax and Revenue:  http://cfo.dc.gov/otr/site/default.asp

Pennsylvania

Pennsylvania Department of Revenue:  www.revenue.state.pa.us/