Yes, Susan Cooper (Dark is Rising-- my favorite series as a kid). A Wrinkle in Time, of course.

Benedict Society.

Flavia de Luce mysteries.

DH loved the Great Brain series as a kid.

Nancy Drew, actually, for HG kids 7~12.

Encyclopedia Brown (I'm sure that's been mentioned).

Alan Gordon's Fools Guild mysteries (not strictly "children's" fare, but they are entertaining and VERY appropriate, and feature an entire family of extremely clever people).




Schrödinger's cat walks into a bar. And doesn't.