Ran across these covers recently and was taken with the title typeface choices:
Rosie and Skate by Beth Ann Bauman (Random House, 2009). A young adult novel about two sisters living on the Jersey shore during the off-season. So 1950s diner-ish. Love the whole cover, actually.
Layla, Queen of Hearts by Glenda Millard, illus. by Patrice Bowman (FSG, release date April, 2010). A middle-grade novel about a girl's friendship with a senior citizen. The red lettering is inviting (for girls, anyway) and the curly style promises a heartwarming story within.
Can an Old Dog Learn New Tricks? And Other Questions about Animals by Buffy Silverman, illus. by Colin W. Thompson (Lerner, 2010). A non-fiction book which examines common sayings about animals and whether they're really true or not. The typeface is energetic, like a comic book; it promises juicy good fun inside. I think boys would think it's rough and tough enough.
I wonder if there are other typefaces that could be sorted into "best for girl books" and "best for boy books" categories.