Hope I'm not too late here, but I've flown from DCA to LIM 14 times in the last 4 years, so I hope I can help. All my flights have been in coach class. Your current choices from WAS are either DCA to LIM through ATL, MIA, EWR or HOU on Delta, Continental, AA, or AA/LAN or out of IAD through El Salvador or Panama (I live in Arlington, so I've always used DCA. The IAD flights always seem to have more connections and cost more, anyway).

80% of my flights to LIM have been through MIA on AA. I've also take Continental through EWR and Delta a few times through ATL, whichever had the best price and connection times for that trip. I've been pretty happy with AA in general, but the leg room is not the greatest. Same on Delta and Continental. I believe AA, Delta and LAN now use exclusively wide body equipment while Continental still uses 757s.

The AA/LAN combo ticket (usually available on Orbitz) is a great ticket to get if it is not too much more than AA all the way. You'll fly AA from DCA to MIA, then LAN Peru down to LIM on the red eye flight. The last time I flew LAN, they were using a brand new 767 with a top of the line IFE system that had an endless choices of movies, shows, music and games all on your own personal screen. Also, LAN has free wine with their meals in economy class.

Hope this helps!

Alan