The LiederNet Archive is a treasure trove of online texts and translations of art songs and choral works --- they claim to be the largest such online reference archive in the world. While the website's look still reflects its 1995 origins, it is the personal project of Emily Ezust and is funded only by donations (make yours here). 

LiederNet is frequently updated and offers a catalogue of 148. 282 vocal pieces and 31,470 transaltions. Be warned: not all the material on the site is public domain and some of it is copyrighted, so have a care when reprinting translations into your recital program.