So, I had to jump in on this one. I had several favorites when I was young.

Here's a link to one of them:

http://www.tias.com/cgi-bin/item.fcgi?itemKey=3923871311

Just a disclaimer -- it was published WAY before I was born. My mom would read it to me and tell me I was like Farmer Hank. I was too young to be insulted and by the time I was old enough to be nostalgic about it, I didn't care.

I also loved Harriet the Spy and From the Mixed-Up Files of Mrs. Basil E. Frank Weiler:

    

These are the covers I remember -- I've never seen the movies and the new covers, meh.