#6 Obsession - See-Saw
.hack//SIGN OP
This has been a favorite of mine for years, so if you're familiar with these top OP/ED lists, you've seen it on mine before in various placements. (I got sucked into this show by the music.) The music is unique, the visuals are unique, and for a show that talks about identity in a digital world, they fit.
#5 Von - Yoko Kanno (starts at 0:29)
Zankyou no Terror/Terror in Resonance BGM
Beautiful and somber music paired with an emotional rollercoaster of a scene.
#4 Trigger - Yuuki Ozaki
Zankyou no Terror/Terror in Resonance OP
Tells a story, introduces the characters, and is just a really nice song, to boot. A near-tie with #3, this is a perfectly-packaged OP.