Register to vote:
Alabama: https://www.alabamainteractive.org/sos/voter_registration/voterRegistrationWelcome.action
Alaska: https://voterregistration.alaska.gov/
Arizona: https://servicearizona.com/webapp/evoter/selectLanguage
Arkansas: https://www.sos.arkansas.gov/elections/voter-information/voter-registration-information
California: https://registertovote.ca.gov/
Colorado: https://www.sos.state.co.us/voter/pages/pub/olvr/verifyNewVoter.xhtml
Connecticut: https://voterregistration.ct.gov/OLVR/
Delaware: https://ivote.de.gov/
District of Columbia: https://www.vote4dc.com/ApplyInstructions/Register
Florida: https://registertovoteflorida.gov/en/Registration/Index
Georgia: https://registertovote.sos.ga.gov/GAOLVR/welcome.do#no-back-button
Hawaii: https://olvr.hawaii.gov/
Idaho: https://apps.idahovotes.gov/OnlineVoterRegistration/
Illinois: https://ova.elections.il.gov/
Indiana: https://indianavoters.in.gov/
Iowa: https://sos.iowa.gov/elections/voterinformation/voterregistration.html
Kansas: https://www.kdor.ks.gov/Apps/VoterReg/Default.aspx
Kentucky: https://vrsws.sos.ky.gov/ovrweb/
Louisiana: https://www.sos.la.gov/ElectionsAndVoting/Pages/OnlineVoterRegistration.aspx
Maine: https://www.maine.gov/sos/cec/elec/voter-info/votreg.html
Maryland: https://voterservices.elections.maryland.gov/OnlineVoterRegistration/
Massachusetts: https://www.sec.state.ma.us/ovr/
Michigan: https://webapps.sos.state.mi.us/MVIC/
Minnesota: https://mnvotes.sos.state.mn.us/VoterRegistration/VoterRegistrationMain.aspx
Mississippi: http://www.sos.ms.gov/Elections-Voting/Pages/Voter-Registration-Information.aspx
Missouri: https://www.sos.mo.gov/elections/goVoteMissouri/register.aspx
Montana: https://registertovote.mt.gov/Application/Welcome.aspx
Nebraska: https://www.nebraska.gov/apps-sos-voter-registration/
Nevada: https://www.nvsos.gov/sosvoterservices/Registration/Step0.aspx
New Hampshire: http://sos.nh.gov/HowRegVote.aspx
New Jersey: https://www.state.nj.us/state/elections/voting-information.html
New York: https://dmv.ny.gov/org/more-info/electronic-voter-registration-application
North Carolina: https://www.ncsbe.gov/voter-information/vr-form
North Dakota: https://vip.sos.nd.gov/pdfs/Portals/votereg.pdf (no registration)
Ohio: https://olvr.sos.state.oh.us/
Oklahoma: https://www.ok.gov/elections/Voter_Info/Register_to_Vote/
Oregon: https://secure.sos.state.or.us/orestar/vr/register.do?lang=eng&source=SOS
Pennsylvania: https://www.pavoterservices.pa.gov/Pages/VoterRegistrationApplication.aspx
Rhode Island: https://vote.sos.ri.gov/
South Carolina: https://info.scvotes.sc.gov/eng/ovr/start.aspx
South Dakota: https://sdsos.gov/elections-voting/voting/register-to-vote/default.aspx
Tennessee: https://ovr.govote.tn.gov/
Texas: https://www.votetexas.gov/register-to-vote/
Utah: https://secure.utah.gov/voterreg/index.html
Vermont: https://olvr.sec.state.vt.us/
Virginia: https://www.elections.virginia.gov/voter-outreach/
Washington: https://weiapplets.sos.wa.gov/MyVote/
West Virginia: https://ovr.sos.wv.gov/Register/Landing#Landing
Wisconsin: https://myvote.wi.gov/en-us/RegisterToVote
Wyoming: http://soswy.state.wy.us/Elections/RegisteringToVote.aspx
If you find any mistakes, please alert @iisaphd69