Kadokawa is releasing five character books:
Haruhi and
Mikuru on April 10, the last three will follow in the next months.
ETA:The
Yuki and
Kyon & Itsuki character books will be released on Mai 9.
ETA: They are also releasing
volume 8 of the manga and an
anthology (?) (both March 26) as well as an
artbook by Noizi Itou (April 24).
See
http://www.kadokawa.co.jp/sp/200603-04/ and
http://www.kadokawa.co.jp/title/index.html?t_id=000003.