IMO - everything is a trade off. If you don't decend long downhills at high rates of speed - drop the discs for cantilever brakes. Pauls canti's are much lighter than any other alternatives. If you aren't concerned with flats - run super lightweight tires and tubes. As for wheels - DaVinci wheels are about the lightest handbuilt wheels i've seen at1,958 for the set and they run WI hubs. Their cranks are also some of the lightest tandem cranks out there as well. Next lightest i've found are the old FSA CF with ti bb's. Of course your talking gram counting here. Switching to Egg beater pedals with ti spindles will also save alot of weight as well. Bars, posts and small items aren't going to get you much for your $$$.

The next thing is to go with a much lighter frame - such as a Calfee CF or CoMo Macchiato.

You can discuss grams or you can discuss pounds. You can discuss hundreds of dollars or thousands of dollars. It all depends on what you want. I hate changing flats - so I use heavier tires and tubes. I like having all the brake I can have when doing long fast downhills at over 60mph so I have a rear disc (and want a front regardless of the added weight). I'm willing to have extra weight for those things.