I have so many favorite anime OP/ED. One of my most favorite would be Rise by Yoko Kanno. And then all of the Inuyasha openings/endings, with a few exceptions. The first ending theme for Inuyasha makes me feel reminiscent of my junior high years as it was airing. The Ergo Proxy themes were awesome as well! Last Exile, Scrapped Princess, and Mai-Hime too! ALL AWESOME.
Anime fighting game BlazBlue CS Second edition opener.
Spoiler:
Gosick
Spoiler:
Dragon Crisis
Spoiler:
Puella Magi Madoka Magica
Spoiler:
FMA Opening 4
Spoiler:
Baka to Test Opening
Spoiler:
Amagami SS Opening 2
The list is much longer than this. Almost every anime I've watched (except Naruto, Bleach, Detective Conan, those types of animes...) I've got their openings pretty memorized. I feel like a nerd.