I definitely think Star Trek, X-Files, and The Twilight Zone belong. As much as I love Buffy, I don't know if it belongs; I think I'd more like to see Firefly on there considering the way that it has of making people sing along when they watch an episode.
If the Doctor Who theme is much the same as the theme used in the version of the show broadcast on The SciFi Channel, then it's ok, but it's not some big ear-catching piece of music to me. I've never heard the themes for Red Dwarf, Thunderbirds, Quantum Leap, or Hitchhikers.
I wonder how some of it is categorized; like does Star Trek include all series, or just the original? If it's just the original, I would think that The Next Generation should also be on the list. As for Babylon 5, as different as each individual seasons' themes sound, they are all variations of the same music. Even with seasons three and five sounding quite different, they are derived from the same basic theme. But if the entry for Star Trek can include both the original and TNG, then a listing for B5 could include all five variations.
I would also submit the theme from Farscape; it's so weird and out there that it really sticks in my mind. I must admit, I'm glad Stargate isn't on this list. I saw another list last week or so of some website declaring the "top 11" scifi villainous species of all time; that list omitted the Shadows of B5 and even the xenomorphs of the Alien series, but included multiple aliens from Stargate. Stargate might be fun, but it's not monumental.