Some more anime openings from the 2000s:
One of my favorite anime openings: Busou Renkin: Makka na Chikai
This one too: Ueki no Housoku: FALCO
That song is nice and cute: Mahoraba ~Heartful Days~ : Daiji daiji
that song really fits the anime: Majin Tantei Nougami Neuro : Dirty
good anime, a little crazy, but with a fitting theme song: Spiral : Kibouhou
the anime is just a teaser for the original Eroge, but the song is better than the game opening: Wind ~ a breath of heart ~ : Feel on the wind