I love this interactive map at Forbes.com! You can enter any major metro area, or county, in the search box, and a map will pop up showing where most of the residents are moving from, or moving to, when they move in or out of the area.
My favorite two searches: Miami/Dade County vs. Collier County (the Naples & Fort Myers area) in Florida. Why do East Coast residents traditionally choose the Atlantic Coast and why do Midwesterners typically choose the Gulf Coast?
Because I-75 runs from the mid-west straight down the gulf side, and I-95 runs from the Northeast straight down the Atlantic Coast.