Here's a prayer for Tisha b'Av, written by Rabbi Zalman Schachter-Shalomi, a.k.a. Reb Zalman.
This comes from the Reb Zalman Legacy Project blog; in this post he explains the origin of this prayer. It's meant to be recited on Tisha b'Av, the day when we mourn both fallen Temples, which this year begins on Saturday, July 28, at sundown. I find it both beautiful and meaningful; I hope you do too.