Join Date: Mar 2010
Location: East Coast US
Bikes: Univega Ultra Sport, old Trek MTB beater
I wouldn't call DC a "great biking city". An "okay biking city", perhaps. I live near DC and for a while my girlfriend lived in the city - theft was an issue. Not so bad as many other cities, but (for example) she got her skewers stolen. And the bike lanes are few - I recall Q street having one (?), but I narrowly escaped being doored three times in one day.
Sounds like the thing you're looking for is a hybrid or a cruiser. Either of the ones posted would work fine. Be sure to ride the bike you're about to buy before handing over money. Also, if there's a choice between shop A and shop B, and shop A has prices that are worse by fifteen or twenty bucks but shop B will spend time watching you ride, making suggestions, and adjusting sizing - go with shop B. Fit/etc. are essential.
Finally, there is at least one co-op in DC (probably more than one.) If you have more time than money, and/or have a desire to really know what makes your bike tick,* a co-op would be worth looking into. They generally have a setup by which you volunteer hours fixing bikes and earn parts by doing so, until after a while you have both a full working bike and a full working knowledge of bicycle repair.
*If your bike is ticking, it's probably the freewheel mechanism.