Right now, Bear McCreary is number one. His work on BSG was so original, creative, emotional, different, powerful, memorable... I have the soundtracks and never grow tired of hearing them. He's made a powerful impact and really showed how great music can impact a TV series.
I also really like Michael Giacchino, whose work includes Alias, Lost, M:I:III, The Incredibles
and Star Trek
Christophe Beck's contributions to the early seasons of Buffy the Vampire Slayer
were pretty good, too. I have a lot of his tracks.
Of course, I still have love for more well-known icons such as Jerry Goldsmith, John Williams and Danny Elfman. Their fantastic work is legendary.