First, be aware that "UL" implies that ALL your gear except food, fuel, and water weigh under 10 lbs. For someone who is newer to backpacking (and the phrasing of your post implies this), this may be a bit overly ambitious, especially for an extended hike like the AT (and yes, I thru-hiked in '99 and have section hiked a number of my favorite section in years since).
So with the idea of "lightweight" gear in mind, some good options to consider would be some of the cottage gear companies out there. ULA Packs
immediately come to mind as thru-hiker approved options. The Catalyst, their largest pack, is still under 3 pounds and will definitely handle a typical thru-hiker load.
Tarptents are likely worth the money to a thru-hiker and Six Moon Designs
makes excellent options. My favorite is the Lunar Solo (e), a solo tent with full bug netting and bathtub floor for 27 ounces (with the heavier
If you start without these, you may wind up kicking yourself when you see them 30 miles up the trail at Mountain Crossings at Neel Gap. This is one of two AT outfitters that carry gear from the two companies.
Two of the big benefits of the AT is the shelter system and the abundance of other hikers (though the sheer numbers may not seem like a benefit until you need help or crave company). But these options give you a reasonably dry place to recover after continuous Spring deluge and the other hikers provide a sort of built-in safety net.
Feel free to PM me if you have further questions and also consider posting on Whiteblaze.net. However, be aware that Whiteblaze tends to be MUCH more active and MUCH more volatile than the folks here. It's a wealth of knowledge once you get past the many varying attitudes.
Best of luck and good hiking!
P. S. It's good to watch your gear weight, but don't make it the end-all-be-all of your hiking prep. After 3-6 weeks, your level of conditioning will be such that pack weight that is merely reasonable, but by no means UL, will no longer be an issue at all. And most importantly, your thru-hike is about YOU and your hike, not your gear. IMO, the best gear is the stuff you never think about, because after a few weeks, your gear won't really matter as long as it works. If you're thinking about it, it's probably broken...... <img src="/forums/images/graemlins/blush.gif" alt="" />