Seatpost: I like Thomson. They're aluminum, and 2-bolt micro-adjust. A little pricy, but they'll last forever, and I love how easily you can adjust tilt on a Thomson. You will need to know a) the length of your current post and b) the diameter that your frame needs. One or both of these are probably stamped on your current post (if it hasn't been cut down, that is).

Handlebar: Everything that you need to buy a new one with the same dimensions is right there in the spec for the old one. I usually look at Salsa for bars. Lots of choices for carbon out there now, or you could stick with aluminum.

Before you buy a bar with the intention of cutting it down, double check the width between your shifters. On some 31.8-clamp bars, the bulge for the clamp is so wide that us petite people can't get the shifters in far enough to allow the grips to fit when the bars are cut. I had a Ritchey that was problematic in that sense (now on DH's bike!), but neither my Salsa or my BBB has been an issue.

Stem: You'll need to know how long the current one is, usually measured from the center of the top cap to the center of the handlebar. I wouldn't get too stressed about angle, as long as it's not a 20* stem or something really upright. Make sure that the clamp size of your stem match the clamp size of your bar, and that the clamp for the steerer tube matches what's on your fork. Almost everything these days uses a 1 1/8" steerer tube. Both Thomson and Salsa make nice stuff as well.

Have fun shopping!