I have several shows that I enjoy watching when I can... My general genera is Science Fiction, but I honestly enjoy just about anything...
Ghost Hunters, Ghost Hunters International, Most Haunted all deal with the paranormal; Most Haunted is a show by Brits, and can be really interesting to compare to the American versions when they all deal with the same content... Basically a "team" goes and explores a haunted place (castle, house, hotel, morgue, hospetal, etc) and they document their experiences and document what was read out on their equipment... It can be really interesting at times, especially when equipment goes crazy then slightly later someone has an experience... I'm not saying that I buy everything I see, but it's great to see the cast's reactions...
Stargate SG1, Stargate Atlantis - I've been watching both of these shows since they first came out... SG1 has been decommissioned however (:sad panda:). These delve into earth discovering other planets through a large gate (called the "star gate"), this gate was created by an advanced race which has "vanished". Initial episodes generally revolved around Earth freeing "enslaved" worlds by a race of symbiotic beings called the Goa'old (basically parasidic beings that take over humans). It's a little far fetched; but quite entertaining...