Mine is 23 lbs (with a freecoaster.  Heavy hubs).  My friends is 20 with no ti and it's super solid.  If you're looking at a complete.... around 24/25lbs isn't unreasonable for a highish end one.  Pretty much everything is under 30 though.
Some easy upgrades to lighten you're bike include swapping the seat, getting some kevlar bead (foldable) tires, taking off brakes (if that's your thing), and swapping to plastic pedals.
If you want to spend more you can look at wheels (lighter hubs, down to 36 spokes rather than 48 if that's what it came with), lighter cranks, bars, forks, stem.
If money is no object you can get pretty much anything titanium now.  Cranks, frame, spokes, hardware, spindles, axles, etc.....
Hope that helps.