I double majored biochemistry and art history. I love art, so I majored in art history as a mental break from science. Definitely do it if it is something that you will enjoy and not just to pad an application as @Strigon stated earlier. I almost tripled majored with Biology. I took so many Biology classes because a guy I liked was a Biology major (I know, but hey, 10 years and still going strong). My Biochem degree was in the Chem department, so it was harder and did not have a lot of bio, which would have allowed me to do the extra bio major, but it probably would have just looked silly.