Although it hasn't been updated for a few years now, this is one of the largest archives of CLAMP related fiction. It has separate sections for both Tokyo Babylon, X and Subaru/Seishirou.
A fanfiction collective, ran by Sephy and Amet. The perfect place to go for some general CLAMP and/or Kamui/Subaru goodness. The unfinished "Gravity" is a definite recommendation.
A number of great Tokyo Babylon and X pieces of fanfiction by Leareth. "Nukume Dori" is a particular favourite of mine.
Firecat has wrriten some great fics focusing upon Subaru, including 'Sakura and Snow' (S/S) and 'Wings' (K/S).
Contains a number of CLAMP-centric fics, many of which are for Tokyo Babylon and/or X.
This fic focuses upon the developing relationship between Subaru and Kamui.
