Significant algorithm from CS for DrRacket that emphasize cons, car, and cdr
I learned Racket using the material taught by the UW MOOC on Coursera Programming Languages, Part B, which is modeled after this UW course.

Here are the relevant helpful documents, which do provide an introduction to the language along with quite advanced material which involves implementing a programming language within Racket:


Notes for Unit 5 and Unit 6
Homework 4 and Homework 5 


The materials in this course are heavy on recursion, so some of the earlier exercises in Homework 4 may help your students with this concept while getting them comfortable with basic Racket exercises.

I also can't speak highly enough of the free, self-paced course materials for UC Berkeley's CS61AS found on the "Textbook" tab. 

These two additional resources may spark some ideas as well:


Example programs in Racket
A* Search in Racket (this relates to one of your other posts as well - two birds with one stone?)