Since early in college, my 2nd choice has always been psychology -- so much that I went back to school to finish up a BA in Psychology. I would focus on either cognitive or industrial/organizational psychology. With cognitive, I'd focus on motivation. With two children, I'm always wondering what motivates them to do the things they do. In I/O, I'm looking at workplace optimization and comfort -- mostly comfort.
On a related note, there is huge world wide need for BCBAs in developmental and behavioral psychology to help expand ABA and other early intensive intervention programs.
