Tower --- the DC tower in Foggy Bottom has a decent selection of both vinyl and CDs but last time I was there they looked to be cleaning out the section!?! Try the Tower at Landmark Mall in Alexandria in Virginia because I'm almost positive they will have most of what you're looking for.
Music Now -- great selection of headz hop (i didn't use trip) on vinyl and some cool CDs; it's in Georgetown in DC
Orpheus -- also in Georgetown, even though they won't have what you want they have a great selection of jazz
GO! -- in Arlington, Virginia; they will have most of what you want on CD and possibly some of it on vinyl.
If your friend wants something to do while they are here there is a great club at 18th and Connecticut NW called the 18th Street Lounge with lots of vibes and a-j
Good Luck!
Keith KWILLIS@vms1.gmu.edu