If you enjoyed Letters on Happiness, here are some other works you might like.
First, the Roman poet Lucretius wrote a long poem on Epicurean philosophy entitled The Nature of Things, which A.E. Stallings has beautifully translated into English (hers is the version I quote from in the dialogue). Another ancient poet influenced by Epicurus was Horace, whose most Epicurean-minded poems I have translated in my collection Ancient Fire (2000). Other poets of an Epicurean bent include Catullus, Tennyson, Swinburne, and Pessoa.
Both The Epicurus Reader and The Essential Epicurus provide English versions of the few writings of Epicurus that survive from antiquity. My own translations of his fragmentary texts on the good life can be found at http://www.monadnock.net/epicurus/.
Letters on Happiness is the fifth volume in a six-movement suite of books I'm writing on the art of living:
Peter Saint-Andre > Writings > Letters on Happiness > Further Exploration