In an attempt to keep this topic alive,
what's your favorite song(s) from Kamen Rider?
all of Den-O(with Yume De Aeta Nara, and double action strike form being personal favorites)
supernova, this love never ends, and individual system from kiva
ranbu escalation, and raise up your flag from Gaim
life is showtime(seriously such a good theme) Wizard
anything goes OOO
cosmic mind Fourze
Journey through the decade, Decade(though I haven't actually watched the series yet, the theme is good enough on its own to be here)
and honorary mention(because a good quality full version isn't out yet) surprise drive, Drive(it sounds so good).