In the latest chapter (217), there was this girl in what seems like a japanese school uniform. Is she the girl from Cardcaptor Sakura? Also, which mangas are connected to this one?

I guess it's Sakura, one from a paralel world (Card Captor Sakura's world).

As for the manga connected to Tsubasa: Recevoir Chronicle you can check in the "Related series" in the manga info page (click the link). I would say the ones more related, in order would be xxxHolic, Card Captor Sakura and X (only for some side characters though, doesn't have the same weight as the ones mentioned before).

This week's favorites:

• Golden Kamui

ççççççç[Ô.Ô] tsutopodus© will eat your manga and steal your cats!

To tell the truth, most of CLAMP's characters appear in TSR at some point or another. I'd say xxxHolic and CCS are the two most related, though mostly for background purposes.

If you've ever thought or said "Nice Guys finish last" and really meant it, then you should probably read this LJ post by DivaLion. It's incredibly insightful whether you're male or female.

From a bumper sticker I like:
"If you're gonna ride my ass, at least pull my hair."

Okay so CLAMP stayed true to their word that it won't be related to CCS at all.
Real|Syaoran's mom, one of the Sakuras we know, isn't the CCS Sakura. It was the Sakura that mom Sakura met that was the cardcaptor.

CCS, I guess, is kinda connected in some way to Tsubasa, since Sakura appeared to give the wand that mom Sakura used to pay the price to Yuuko. xxxHolic is also connected, since the events happening there are on the same time as the events happening in Tsubasa.

Well, and the whole 'Watanuki / Syaoran' thing. (Not saying more than that to avoid spoilers.)

If you've ever thought or said "Nice Guys finish last" and really meant it, then you should probably read this LJ post by DivaLion. It's incredibly insightful whether you're male or female.

From a bumper sticker I like:
"If you're gonna ride my ass, at least pull my hair."