Classroom Peanuts
by Charles M. Schulz (Holt, Rinehart, and Winston, 1982)
A 200-page large-format compendium, five black-and-white dailies or one colour Sunday per page. Peppermint Patty and Sally feature most often, and school is where Sally is at her funniest. Given how wearisome themed collections can be, this one holds up remarkably well.
The Complete Peanuts: 1971 to 1972
by Charles M. Schulz (Fantagraphics Books, 2009)
An evocatively drawn mix of wit, whimsy and preternatural wisdom. Poor old wishy-washy Charlie Brown remains the unifying figure but there are a good number of delightfully droll (and character-defining) strips involving Peppermint Patty, Sally Brown, and in particular Lucy van Pelt.
The Complete Peanuts: 1979 to 1980
by Charles M. Schulz (Fantagraphics Books, 2011)
An excellent vintage. As well as his usual pithy one-offs, Schulz presents several week-long serials and even one month-long epic. Peppermint Patty comes particularly to the fore, validating the claim that she could have sustained a comic strip in her own right.