Listed below are links to the I.R.S. and all 50 State Department of Revenues:

Federal
1 Internal Revenue Service http://www.irs.gov/
States
1 Alabama http://www.revenue.alabama.gov/
2 Alaska http://www.revenue.state.ak.us/
3 Arizona http://www.azdor.gov/
4 Arkansas http://www.dfa.arkansas.gov/
5 California http://www.ftb.ca.gov/
6 Colorado http://www.colorado.gov/revenue
7 Connecticut http://www.ct.gov/
8 Delaware http://revenue.delaware.gov/
9 Florida http://dor.myflorida.com/dor/
10 Georgia https://etax.dor.ga.gov/
11 Hawaii http://www.state.hi.us/tax/
12 Idaho http://tax.idaho.gov/
13 Illinois http://www.revenue.state.il.us
14 Indiana http://www.in.gov/dor/
15 Iowa http://www.iowa.gov/tax/
16 Kansas http://www.ksrevenue.org/
17 Kentucky http://revenue.ky.gov/
18 Louisiana http://rev.louisiana.gov/
19 Maine http://www.state.me.us/revenue/
20 Maryland http://www.comp.state.md.us/
21 Massachusetts http://www.mass.gov/
22 Michigan http://www.michigan.gov/treasury
23 Minnesota http://taxes.state.mn.us/Pages/index.aspx
24 Mississippi http://www.dor.ms.gov/
25 Missouri http://dor.mo.gov/
26 Montana http://revenue.mt.gov/default.mcpx
27 Nebraska http://www.revenue.ne.gov/
28 Nevada http://tax.state.nv.us/
29 New Hampshire http://www.nh.gov/revenue/
30 New Jersey http://www.state.nj.us/treasury/taxation/
31 New Mexico http://www.tax.newmexico.gov/
32 New York http://www.tax.ny.gov/
33 North Carolina http://www.dornc.com/
34 North Dakota http://www.nd.gov/tax/
35 Ohio http://tax.ohio.gov/
36 Oklahoma http://www.tax.ok.gov/
37 Oregon http://www.oregon.gov/DOR/
38 Pennsylvania http://www.revenue.state.pa.us
39 Rhode Island http://www.tax.ri.gov/
40 South Carolina http://www.sctax.org/default.htm
41 South Dakota http://www.state.sd.us/drr2/
42 Tennessee http://www.tn.gov/revenue/
43 Texas http://www.window.state.tx.us/taxes/
44 Utah http://www.tax.utah.gov/
45 Vermont http://www.state.vt.us/tax/index.shtml
46 Virginia http://www.tax.virginia.gov/
47 Washington http://dor.wa.gov/
48 West Virginia http://www.wvrevenue.gov/
49 Wisconsin http://www.revenue.wi.gov/
50 Wyoming http://revenue.state.wy.us/