It's already been said twice, but I highly, HIGHLY recommend Supernatural. It follows two brothers as they travel the U.S. killing every paranormal creature you can possibly imagine. They also keep fairly accurate to the legends, so if you are a mythology buff like me, it isn't a painful experience. There is also a very interesting, very awesome under-arcing plot that has finally come to fruitation now (fifth Season).
Criminal Minds is a good show if you like crime shows and you don't mind getting the details of a case of a deranged killer and all the disgusting things he/she does to his/her victims. It's a show about a team at the BAU, a special branch of profilers that help catch serial killers. The characters are very rounded and believable, and you will probably grow to love them. (currently in its fifth season)
