As you can see starting a thread like this is risky. But I'm an unabashed weight weenie, so here's a description of my lightest road bike, which weighs 15.3 pounds: American Classic 57 cm ti frame (Made by Litespeed), Look HSC 1 fork (Their original all carbon fork I think) w/1" Aheadset, American Classic ti seatpost, 3T Zepp stem & 199 bars w/Cinelli tape, Campy Record Carbon Ergo shifters and derailleurs, American Classic 350 wheelset with Cycle Dynamics ti cogset & ti skewers, Conti Supersonic tires & Race Lite tubes, Topline crankset & ti bottom bracket (They've been off the market for a while), Selle Italia Flite TT saddle, Sram 89R Chain, a "very" light brakeset I got from Brew Bikes many years ago, Bebop pedals, and of course the usual assortment of ti hardware. I've probably got 8,000 miles on it.
As far as secret weapons go, when I get some money ahead I'll probably install one of IRD's new CNC'd aluminum cassettes; carbon bars & stem, and an Easton carbon seatpost. That should get me under 15 pounds and that's as light as I can afford to go. However I have been eyeing an Ellsworth Flight frame that's over a pound lighter than my ti frame and though I was only been able to pedal it for 50 miles, it seemed to have a steel/ti-like ride.
In response to 55Rad, do you mean the four bikes listed weigh less than 75 pounds. If so, they need to go a diet (That's a rather hefty average of almost 19 pounds each!?), particularly when you consider the oldest is a '98 vintage, and it's a piece of cake to build 16 - 17 pound bikes these days (Did I mention you also need to be a bit thick skinned to start or respond to a thread like this). A quick review of my "N+1" bike inventory indicates 75 pounds gets you the road bike described above (15.3), an Ellsworth Id (25.5), a Crotch Rocket single speed mountain bike (18.0), and an Aquila fixed gear/track bike w/Shimano 10 pitch group (14.0), with two pounds to spare.
A final note is there was a sub 10 pound road bike (I think it might have been just a tad over eight pounds!) in the Speedplay booth at Interbike this year. So we can all just shut up.