This is what you're referring to:
If you want to be able to look at DC and the monuments, etc., sit on the LEFT side of the aircraft, i.e. the captain's side. If you want to see the Virginia side, the Pentagon, and DCA
itself (just before you turn short final), sit on the right (F/O's) side. They'll use this approach when the winds are out of the south. If the winds are out of the north, they'll be on a different approach, and DC will then be on the right side, and the other items on the left.
And, most importantly, if you're inbound to DCA and suddenly realize that you're seated on the wrong side of the aircraft relative to what approach/runway is in use and what you'd like to see, DO NOT arbitrarily get up and change seats. If you do so within the last :30 of the flight, post-9/11 regs dictate that everyone must remain seated during this time. If anybody gets up during the last :30, the flight diverts to IAD, and the security folks do their thing.
One thing that you might do is to, upon boarding, ask the flight crew which arrival is (or is likely to be) in use at your ETA. That way, you can change seats (assuming empties on the proper side are available) while enroute, and well before the :30 cut-off.
[Edited 2004-08-15 21:35:16]
ALL views, opinions expressed are mine ONLY and are NOT representative of those shared by Southwest Airlines Co.