I have a soft spot for Kaleido Star. Soemthing about it was just great, but I really can't put my finger on what.
Just ordered Sound of the Sky recently and I'm sure I'm going to love that series too.
Despite my love for music and anime, I just didn't love Beck like everyone else seems to. It's a good series, but it annoyed/bored me at times and I didn't feel it was particularly special.
I've got Scrapped Princess and Kurau sat on the shelf (been there for about 3 years) and no real desire to watch either for some reason.
Other anime I think is underrated:
Noein, Simoun, Nana (well, if Beck counts), Michiko to Hatchin,
Ef (glad to see those series finally getting a western release), Toward The Terra, Figure 17, Fantastic Children... I coudl probably go on for ages but I should probably ghet back to working