Voting Machines by County in the United States...
So I did some googling / sleuthing / lexising and tried to use the EDS' voting technology map to figure out what most of the DREs used in counties in the US are... here's a start... if anyone sees anything obviously wrong or has additional information, please let me know. If you don't know much about DRE voting machines and the different types, stay tuned to the EFF's E-voting Archive where they'll be publishing quick reference guides on all of them.
Below, find voting equipment links by county, cribbing off of EDS' voting equipment map (on page 7). I tried to find what DRE and what county corresponds to the purple color on the map (coded as Electronic). If the state elections official had a decent list of voting equipment, I generally stopped looking there.
(in Alpha order)
Alabama - Baldwin Co. uses Diebold TS
http://www.votersunite.org/info/content/mess-up_082304.asp
Arizona - The automark will be tested there... one county uses DREs... not sure if Diebold or Sequoia.
http://www.azsos.gov/releases/2003/pressrelease46.htm
http://www.azsos.gov/Releases/2004/pressrelease19.htm
Arkansas - Can't find anything on Arkansas even though the EDS map lists a few counties as being DREs.
California (we know this mostly, right? 
):
http://www.calvoter.org/issues/votingtech/0304directory.html
Colorado - a few DREs (Hart, Sequoia, Diebold, ESS), more O/S
http://www.sos.state.co.us/pubs/hava/cty_vtg_eqpt_inv_2004_09_13.pdf
Delaware - all 1242s
http://www.state.de.us/doe_ncc/Use_VM/
Florida - ES&S, Diebold, and Sequoia... (iVotronic counties: Broward, Collier, Lee, Miami-Dade, Charlotte, Lake, Martin, Nassau, Pasco, Sarasota, Sumter. Sequoia AVC Edge counties: Indian River, Palm Beach, Hillsborough, Pinellas.)
http://election.dos.state.fl.us/votemeth/systems/countysys.asp
Georgia - All diebold TS machines
http://www.sos.state.ga.us/elections/electronic_voting/faqs.htm
Hawaii - uses the Hart Intercivic
http://www.hawaii.gov/elections/dre/
Indiana - Lots of ES&S, Microvote MV-464s...
http://www.in.gov/sos/elections/voters/vot_sys.html
Iowa - lots of O/S, MV-464s...
http://www.sos.state.ia.us/pdfs/elections/CoVoteSystem.pdf
Kansas - MicroVote MV-464 is used in Sedgwick County, KS
http://www.sedgwickcounty.org/elections/microvote.htm
Johnson County, KS uses Diebold TS machines (and OS)
http://www.jocoelection.org/Menu-VotingComputers.htm
Kentucky - lots of 1242s, some MV-464s
http://www.sos.state.ky.us/YOUTHPAGE/elecfiles/votingequip.asp
Louisiana - some "AVC" (not sure if Edge or Advantage) some ivotronics.
http://www.sec.state.la.us/elections/elect-machines.htm
Maryland - mostly TSs, Baltimore county uses AVC Advantages
http://www.elections.state.md.us/citizens/voting_systems/md_voting_systems.html
Michigan - Mecosta uses the MV-464
http://sosntsl01.sos.state.mi.us/votesys/votesys.asp?code=54
Allen township and Tecumseh city uses an older Unilect machine
http://sosntsl01.sos.state.mi.us/votesys/votesys.asp?code=30
http://sosntsl01.sos.state.mi.us/votesys/votesys.asp?code=46
Mississippi - Hinds county, MS uses Hart eSlate (there's two other counties with DREs but I could pinpoint the counties or DREs)
http://www.votersunite.org/info/content/mess-up_070404.asp
Nevada will be AVC Edge machines everywhere but Clark county which will have one VVPAT-enabled Edge per precinct and the rest Advantages.
New Jersey - mostly Sequoia AVC Advantages
http://www.state.nj.us/lps/elections/vote_equipment_list.html
New Mexico - Contacted Charlie Strauss... he will fax a soon-to-be-outdated list of voting equipment in NM. They use Sequoia AVC Edges, Some 1242s, and some iVotronics.
New York - seems to be all O/S and New York City is either lever (if you believe the first link) or Sequoia AVC Advantage (if you believe the second):
http://vote.nyc.ny.us/pdf/documents/boe/pollworkers/PollWorkersManual.pdf
http://www.notablesoftware.com/Papers/vmrisks.html
North Carolina - tons of different O/S and DREs used
http://www.ncvoter.net/machines.html
Ohio - it's a mess, I'll ask Dan Tokaji ...
http://moritzlaw.osu.edu/electionlaw/equipment_machines03.html
Pennsylvannia - (Mercer, beaver and Greene counties use Unilect. Potter and Montgomery use Sequoia AVC Edge. Dauphin, Berks and Philidelphia counties use 1242s.)
http://www.hava.state.pa.us/hava/cwp/view.asp?a=1188&q=442396&votingNav=|
South Carolina - statewide purchase of iVotronics
http://www.scvotes.org/
Tennessee - lots of different things... DREs... O/S...
http://www.state.tn.us/sos/election/votingmachines.pdf
Virginia - All sorts of O/S and DREs
http://www.sbe.state.va.us/Election/Voting_In_Va/votingequipment.htm
Wyoming - a couple DREs... (1242, Diebold)
http://soswy.state.wy.us/election/systems.htm