For HVAC, we have been pleased with Delta Service Co. (703-550-5520). My parents have used them for at least 30 years now, and based on their recommendation I started using them when I moved into my house back in 2001. Very reliable and honest people. I like it that they call to tell you when the workman is on his way—that is, if you make an appointment for, say, Friday between 2:00 and 5:00, when the workman leaves to come to your house you will get a call saying "the man's on his way" (always in those words!).
Only downside is they do not take credit or debit cards. That was a potential issue for us last fall when we replaced our AC, furnace, and thermostat. But they do take those credit-card promotional checks. I had a fee-free check offer whose interest rate was lower than my card's standard rate, so we used that to pay for the work and then paid it off over three months.
For plumbing, we use the Irish Plumber (
http://www.theirishplumber.com; the website has a coupon). I don't know whether he goes out to Loudoun County. We discovered him from an ad on the back of a church bulletin one Sunday morning when the disposal clogged and sent water fountaining all over the kitchen. The owner is indeed an Irishman with a great brogue. They've replaced our hot water heater and three toilets and they've always done good work. They do take credit cards, BTW (at least VISA and MasterCard, anyway...don't remember whether they take Amex, but I'm guessing not because I usually use it if it's accepted).
Edited to add: BTW, when we replaced the HVAC, Delta's estimate came in about $4,500 lower than Cropp Metcalfe's, and that's prior to the $1,025 mail-in rebate we got from Carrier. I was impressed with the guy from Cropp Metcalfe, but that sort of price difference is simply too much money to ignore!
