Shimano 600, 105 Campy Chorus and Campy Athena stuff, from the 8spd days are all very affordable and, minus the 105, look the part of high-end componentry. That said and done, the best bargains for modern stuff are:

Cranks: Shimano 105, Sram Rival and Ultegra (5600 and 6600). For some weird reason, these things sell for under $100 all the time.
Brakes: Shimano 105, and Campagnolo Centaur grey. $50 for pretty heavy but superbly functional dual pivots. Brand new.
Brake/Shifters: Campagnolo Centaur and Shimano 105. Under $125 new if you're patient.
Wheels: Neuvation, Ritchey Protocol and Shimano 5600's: Look hard enough and the Shimano's can be had for $150. Ritchey's @250-300 and the Neuv's starting @ $200
Rear derailleurs: Shimano 105 5600 @$ 40 shipped, Ultegra 6600 @$50, Ultegra SL @$62. All brand new. Dura Ace 7800 for $62 if you can stand a small scratch or two.
Front Derailleurs: Look hard for your brand (and level) of choice and you'll find deals everywhere. I bought a Dura Ace 7800 used for $15 shipped.

Danny