I just had a reference question about how to find a quality translation of an aria from the original Italian into English. The Aria Database has been listed on our Music Research Guide for a couple of years and I just found another good place to find some of these.
The Lied and Art Song Texts Page has thousands of quality translations and, with its focus on lieder and other art music, it serves as a nice compliment to the Aria Database. The site gives the user the ability to browse through thousands of texts by composer, poet, first line, title and language.
As always, if you need help tracking down a translation, check with us at the Ask Here desk.