Go Ask Alice (by an Anonymous author) is frequently cited for drug references, offensive language, and for being sexually explicit. It was among the top 10 most frequently challenged books for 2001 and 2003, and was 25 on the list of 100 most frequently challenged books: 1990–1999 (and shot up to 18 for the same list, 2000-2009).The Golden Compass by Phillip Pullman was challenged for its "religious viewpoint" in 2007.
In the Night Kitchen by Maurice Sendak. Challenged for "nudity, offensive language, [and] sexually explicit" material, it's on the list of 100 most frequently challenged books: 1990–1999.
Crazy Lady by Jane Leslie Conly, which has been challenged for its offensive language on both top 100 lists (1990-1999 and 2000-2009).
More information on these challenges can be found here, here, and here. [see Blog Policy Information.]