Washington DC
Here ya go! Hope this helps and if your nervous and need someone to go with you, just PM me... 
Testing Locations
Sure! A quick google search is all I did, not sure of which area you are in, I go to places I know in DC mostly because it's like a place on every corner, and when you go, they report the number of ppl they help to get funding for programs and services. Planned Parenthood does testing for men and women, a lot of ppl don't know that! but there may be a small fee for STD testing. So, here's a brief list of links:
IN PG COUNTY: http://www.princegeorgescountymd.gov/Government/AgencyIndex/Health/hiv.asp?nivel=foldmenu%284%29
IN MONT. COUNTY: http://www.montgomerycountymd.gov/hhstmpl.asp?url=/content/hhs/phs/index.asp (they say they require residency proof, IDK)
IN BMORE COUNTY: http://www.baltimorecountymd.gov/Agencies/health/healthservices/hivsites.html
IN DC: http://doh.dc.gov/doh/lib/doh/services/administration_offices/hiv_aids/pdf/testingcenters_0607.pdf
From my experience, you do not need residency or an appt in any particular area to get tested, you just need your photo id. Most places have the oral swab HIV test and counseling available while some have services that will test for other STDs through urine or blood- the HIV results you should get the same day!
Check out stdlaert.com - You set it up anonymously online, make an appointment with a local lab (LabCorp, I think) with whatever name you'd like to use. Come to your appointment; no ID is required (but be prepared to answer a question or two about the form you filled out, like whatever birthday you reported on the form; the techs are just trying to verify they have the right person in the chair). Leave blood and urine samples for a complete panel. There are a variety of testing packages but a full panel to check everything is about $235, so you'll need a credit card you're comfortable charging this to; the billing entry is fairly innocuous. The payment is done online. A few days later your results come back to you in a PDF lab report on whatever email you specify. It's about as anonymous as you can get.
The full panel includes tests for -
Chlamydia
Gonorrhea
Hepatitis A, B and C
Herpes I and II
HIV I and II
Syphilis
You can also elect to test for fewer STDs or even a single STD, but why not do the whole thing? For less than what you'd pay for an appointment you can have some peace of mind. I've used this service and I've been very satisfied with it. Fortunately, results have always been negative. But if any tests do come up positive, you can act on those results quickly and save yourself and possibly others from some serious health issues.