xxxHolic, by the ever-famous and infinitely talented CLAMP. CLAMP is the group of women behind classics like X/1999 and Magic Knights Rayearth.
xxxHolic in anime form is only slightly tied in with the animated version of Tsubasa and Card Captor Sakura, so if you don't know either of these stories well (I don't), you can still follow the anime quite easily. Tsubasa and xxxHolic tie together again for the movie-length ending to the anime series. Honestly, I love the anime version and the manga version for different reasons, and they are very different from each other in content (as opposed to, say, Black Butler, which is virtually identical to the manga version). The manga is a bit more morose, sorrowful, and introspective. It's quite a powerful story. The anime, however, is mostly light-hearted and funny.
Like any obake/yokai story, it's full of Japanese superstition mixed with modern and foreign ideas; however, I think it stays somewhat true to Japanese superstitions, which I enjoy. Japanese ghost stories are very creative, and the yokai are imaginative and varied, unlike how some Christianised European culture has distilled them all down to mere minions of Satan hiding in bushes or something.
Watanuki, our main character, is a whiny, over-reactive teenage boy with a talent: he can interact (and see) yokai/demons/spirits. It is a talent he hates. He lives alone, as both of his parents have died. By fate, he meets Yuuko, the Dimensional Witch (it's a rough translation, I think). She is a granter of wishes; you cannot see her shop unless you deeply desire to have a wish granted. Watanuki becomes indentured to her for an indefinite period of time in order to buy his ability to never see yokai again.
Along the way, he must learn a lot about people, about the nature of yokai and spirits, wish-granting, and all sorts of things. Naturally, he is forced to become aligned with a person who he doesn't really care for and views as competition, but the 'competition' has no ill-will towards Watanuki. And the ever-cute Himawari is totally clueless and has no idea that Watanuki is freaking out about liking her half the time. Yuuko and I have much the same attitude about life and people, so maybe it helps me love it even more...
Sadly, the series only lasts 24 episodes plus the movie, so it never has a chance to get into why Yuuko is bothering to teach Watanuki the things she is instead of simply hiring him as a maid or somesuch. For that, you'll have to read the manga, which is absolutely wonderful. But really, I suggest you see both- the colour and brightness of the anime, the seiyuu, it's just... <3 And how in-depth the manga gets! It's so worth it! For those of us who don't have $150 to just rush out and buy a series, may I recommend reading it online? It's addictive! Don't start this on your lunch break!