Some of the first Code Geass openings didn't really do it for me because of the music, but I really liked O2 when they brought it along.
Kaidoku Funuo is great too.
Edit: Also, I agree Soeroah! Code Geass was most excellent and, while I didn't like all the opening songs, the way they change with the plot is great. When I watched it, I thought it was just going to be some lame kind of ending, but my mind was blown.