There will be a new Haruhi Concert on April 29, 2009, "Suzumiya Haruhi no Gensou".
It seems to be a classical concert with the Tokyo Philharmonic Orchestra directed by Philip Chu, and with Seiji Honda (piano) and Hiroaki Yura (violin).
Aya Hirano and Chihara Minori are listed as guests.
http://www.haruhi.tv/fanclub/special_event_gensou.html