His works are hard to come by [for free and in their entirety] on the internet. Here are a few of them:
http://www.scribd.com/doc/23436847/Writings-and-Sermons-of-St-Peter-DamianContents:
• The Book of the Lord Be With You
• On the Perfection of Monks
• Sermon For the Feast of the Epiphany
• Sermon for the Vigil of St. Benedict
• Sermon on the Discovery of the True Cross
• Sermon on the Holy Spirit and His Grace