If you travel a lot and get to the airport expecting a two-hour check-in / security clearance process and end up doing it in 15 minutes, the lounge is an excellent investment. Unfortunately, the place is usually packed with people who anticipated the same thing.

If you get a stand alone Amex Platinum Card, you get comp admission to NW and CO lounges. If you fly DL and UA, get a DL Crown Room Club card or UA's Red Carpet Club Card and you can access DL's lounges when flying DL and UA's when flying UA in the U.S. only.