On the Beach by Neville Shute would be a great novel to pair with The Road. It is set in a post-apocalyptic Australia during the '60s. The characters know that the end of life is inevitable due to nuclear fallout, and the government even offers suicide pills to ease the suffering.
How about Harlan Ellison's A Boy and His Dog? It's a great story about life in post-apocalyptic Australia with huge doses of dark humor not found in the ultra-serious The Road. Ellison's tale won the 1969 Nebula Award (Best Sci-Fi Novella) and the film version (starring Don Johnson) won a Hugo Award.
Without knowing the parameters of your assignment, I might suggest a comparison to the 19th century novel by Ivan Turgenev called Fathers and Sons (1862). The story traces the experience of who has become a nihilist and rejects his father's ways and the old order of life. Bazarov's tragic and ironic end raises questions about moral responsibility and the correct order of life.
I wonder whether dystopian novels might be a good choice for you to think about for this comparison. Novels such as The Handmaid's Tale and even Lord of the Flies portray worlds where power has been seized by the few and is used and abused to make the lives of those without that power very miserable indeed. Choosing one of these books would allow you to compare the nature of a dystopian novel and what characterises this genre.
On first glance, it might be odd, but I think that a great comparison point between McCarthy's work might be Elie Wiesel's Night. If you are seeking to examine the dimensions of the father/ son relationship in both works, there will be much in way of points in convergence and divergence. I think that one can see a redemptive vision in McCarthy's work and see a more despairing vision in Wiesel's rendering. I think that it might be interesting to see how both writers see the strength of bonds towards family in periods of abject horror and personal struggle. The father/ son relationship in McCarthy's work is a sanctuary from the cruelty of the world. In Wiesel's work, the bond between father/ son becomes victim of the world around it. I think that being able to see how both writers see the strength and eventual withering of such bonds becomes vitally important to each author's view of the world and their fundamental understanding of how reality is constructed in the modern and postmodern setting. It might be a very interesting emotional dynamic to examine each work in how it treats the father/ son relationship.
The Book Thief By Marcus Zusak can be compared through ideologies of truth and Identity. Due to the nature of both books there are many differnt ways you can compare them as there are different view points on them. Such as, are these books, books of hope? Compare and contrast.