What are the names of the books in the series the heros of Olympus?

The third Heroes of Olympus book has not, unfortunately, not come out yet. On October 4th, 2011, though, the Son of Neptune (the second book) will come out, and the title to the third book will be released.

That last answer is way outdated. The Son of Neptune came out already and the third book, The Mark of Athena, is coming out October 2, 2012