I mostly liked Encyclopedia Brown, but you could totally tell that every so often the writer had gotten blocked and had gone looking through trivia books until he found a fact that he'd turned into that particular chapter.

Is The Witch Family the Phyllis Reynolds Naylor series with the sister who was under the spell of the creepy neighbor? Um.. Witch's Sister, Witch Water, and The Witch Herself, if I remember correctly. Oh, no, wait, you said "Not in series." Must be something else. Anyway! The Naylor books were excellently spooky.

Oh, and what about The White Mountains? with the Tripods and the caps... those were good too.