Welcome to the Sakura/CLAMP Fan Club, Glitch! Feel free to post a banner in your sig, but no Clow Cards, please (you can win those through the monthly trivia contests we have!).
People will have varying opinions on this, AngelSakura, but I would recommend Tsubasa Reservoir Chronicle. Actually, that and XXXHolic cross over in their storylines, but you don't need to read both to understand either one. You can just choose one if you'd like. Tsubasa is more fantasy oriented, with a focus on a quest by heroes to save a princess. XXXHolic is more realistic, while still having magic elements, and deals more with human drama--a witch who grants peoples' wishes...for a price. XXXHolic is also darker than Tsubasa, in my opinion. Kirastill, the two titles are still fairly new, but Vol.'s 1 and 2 of XXXHolic and Vol. 1 of Tsubasa are available in bookstores right now. If you have any interest in them after my brief descriptions above, I'd recommend you give them a try, or at least peruse them in the bookstore to see if they are to your liking. As with any CLAMP title, the strorytelling is solid and the art is exceptional.
Glitch, I just pronounce Tsubasa Reservoir Chronicle exactly as it's written, ignoring the capitals.
As for the aforementioned trivia contest, it will be winding down soon, so if anyone out there is looking to catch the Dash card, please get your entries in to me by PM this week! Here are the questions again so you don't have to go searching!
1. What element makes up Hikaru's magic in Magic Knight Rayearth?
2. What is Sakura's official title in Tsubasa Reservoir Chronicle?
3. What does Yuuko promise to do for Watanuki (what wish of his will she grant) in
XXXHolic?
4. Who does Misaki stay with while in Tokyo in Angelic Layer?
5. What is the angel Suzuka's nickname in Angelic Layer?