The rail yard in Clovis, New Mexico is a busy place. It sits along BNSF's southern Transcon route, seeing around a hundred trains a day. If you're tired of sitting by a pair of lonely old tracks, waiting for something to pass by, this is the place to go.
There are two overpasses that allow good views of the yard, and dozens of places near the yard to get a look. Neighboring towns like Melrose and Bovina, Texas also offer good railfanning.