There is a second season to Tsubasa, as well as a movie (unrelated) and 4 ova coming out early next year. The 4 ova tie in with xxxHolic somehow and tie up both shows as far as I know.
As for me I am currently watching D.Gray-Man and am enjoying it so far. Only up to episode 26 atm but its good. Funny at times and the action is pretty decent, could have a little more of it but its not to dry either. Decent story so far too so we'll see how the other 70+ episodes go.
Yeah I was just checking out a little bit on Wiki and apparently xxxHolic is a sister series to Tsubasa. I'm looking forward to watching the second series, and I guess I might have to check out xxxHolic too if I see a box set floating around.
I just finished Tsubasa season 1 a little bit ago. I really enjoy the characters and the music is fantastic, kind of reminds me a lot of .Hack//Sign in some ways (musically). I am glad there is a second season, since the story's far from complete.
Edit: Also, apparently a lot of the characters have a connection to Cardcaptor Sakura (also by Clamp). This is kind of funny, since well the moment I saw Sakura in Tsubasa I had this weird feeling she really looked a lot like the Sakura in Card Captor Sakura, as if the name wasn't a dead give-a-way. But apparently that isn't the only similarity between the two. The king of Clow, Toya, is apparently also in CCS.
Hmm not only that but it looks like Clamp involved several of their other series within Tsubasa. Very interesting. Hehe.
Second Edit: Heh, I've been doing even more checking into since I figured there had to be more similarities between Tsubasa and Card Captor Sakura. I was right. There's a ton of character similarities. Nearly every character that shares the same name between the two also shares a very similar character design and even semi-similar roles. To me this can be seen as either Clamp being highly unoriginal or incredibly ingenious. Either way, it certainly was interesting to realize.