Many of the Galaxy of Fear books have cameos from famous star wars characters. Here's all the ones I know of:

#1: Darth Vader, Luke, Leia, Han, C-3PO, R2-D2 and Chewbacca.

#2: (Possibly all of the above except Vader) Dr. Evazan and Boba Fett

#3: Wedge Antilles

#4: Lando Calrissian and Dengar

#5: Darth Vader, and Dannik Jerriko

#6: Darth Vader

#7: Jabba the Hutt

#8: Grand Admiral Thrawn

#9: ?

#10: Dash Rendar

#11: Darth Vader

#12: Boba Fett, and Yoda

More information will be available when I finish all of the books.