By taxi
You'll have no trouble finding a taxi on M St or Wisconsin Ave any time of the day.
By bus
The Georgetown Metro Connection (http://georgetowndc.com/g...) provides convenient little blue buses with many stops along M St, running between the Rosslyn and Dupont Circle metro stations. Fare is $1, or $0.50 when boarding at a metro station and paying with a Metrorail SmarTrip card. Buses leave from the top of the escalators at the Rosslyn metro station or 19th Street and Sunderland Place near the south exit of the Dupont Circle metro station every ten minutes M-Th 7AM-midnight, F 7AM-2AM, Sa 8AM-2AM, Su 8AM-midnight.
The very convenient D.C. Circulator (http://dccirculator.com/) Georgetown-Union Station "Yellow" Line bus runs along the length of Wisconsin Ave in Georgetown, then along M St towards the West End, where it passes by the White House and then into the East End on its way to Union Station 7AM-9PM daily, every ten minutes.
#38B (http://wmata.com/bus/time...) also connects Georgetown to Farragut Square and the Rosslyn Metro stations. The #G2 (http://wmata.com/bus/time...) runs along P St from the University's main gates to Dupont Circle, and on to Logan Circle.
#32 and #36 (http://wmata.com/bus/time...) run down Wisconsin Ave from Friendship Heights past the National Zoo, then east through Georgetown along M St, then down Pennsylvania Ave to the Mall.
#31 (http://wmata.com/bus/time...) runs from Tenleytown-AU, down Wisconsin, and then along M St. Unlike #32 and #36, which stop near the Foggy Bottom Metro station on Pennsylvania Ave, before the Circle near GW Hospital, the #31 picks up and drops off directly in front of the station.
By Metro
There is no direct Metrorail connection to Georgetown. Georgetown is an easy one-mile walk from either the Rosslyn or Foggy Bottom/GWU Metro stations, and a mile and a half from the Dupont Circle metro station. Walking to/from Rosslyn also guarantees some really nice views from the Key Bridge.
By car
Driving in Georgetown is not a pleasant experience. Streets are clogged, pedestrians are aggressive that's right, the pedestrians, major arteries reverse flow and become one-way during rush hour, and you will usually have trouble finding parking anywhere near where you want to be. Parking is available at Georgetown University for $3/hour or $15/day, or at The Shops at Georgetown Park for $18/day.
Wisconsin Ave and M St are the major arteries. The Whitehurst Fwy from K St is a quick way to get in not out from downtown to M St. The Key Bridge from the west end of M St connects Georgetown with Arlington, Virginia, and continues towards Washington Reagan National Airport DCA and Old Town Alexandria.