Below is a list of resources that I personally use and highly recommend.
The LiederNet Archive - A gigantic archive of text for tens of thousands of songs in countless languages and houses a wealth of information on the composers, poets, and more. I cross-check my transcriptions with texts found here when available.
Art Song Central - A wonderful resource of sheet music links, historical background, poetic texts, and about 60-70 phonetic transcriptions per language.
IPA Now! - Transcriptions found on our website are primarily generated using this software, with editorial corrections either suggested by colleagues/visitors to the website, or by a contributer of this archive.
IPA Source - A paid resource, however, many music schools across the nation have purchased liscences to this invaluable resource. Check with your academic institution to see if it's available to you for free.
The Aria Database - You can find the texts and background information for many arias on this website, all for free.
Exploring Art Song Lyrics - I was most fortunate enough to meet the author (Dr. Jonathan Retzlaff, Eastman) of this book during a NATS internship program that I sang in, after I'd used it for two years. There are translations and IPA transcriptions of well over a thousand art songs. This is an important investment in any serious classical singer's library.
A Handbook of Diction for Singers - This book covers IPA rules for lyric Italian, German, and French, written by CCM faculty member David Adams.
Singing and Communicating in English: A Singer's Guide to English Diction - It is often times most difficult for a singer to sing in their native language. If you're a native English speaker, you may find a great deal of worthwhile information in this book.
Song: A Guide to Art Song Style and Literature - This is probably the single most important book for young classical singers to have at their disposal in my personal opinion. The author, Carol Kimball, provides a wealth of historical knowledge on several hundred pieces.
Art Song: Linking Poetry and Music - Another excellent resource by Carol Kimball.
A French Song Companion - This book provides detailed background information on a great deal of French repertoire, and an excellent resource to discover new literature.
Interpretation of French Song - An absolute must-have for performing French repertoire, Bernac provides his expert advice on a number of popular melodie.
The Fischer Dieskau Book of Lieder - This book contains roughly a thousand translations of German Lied by the famous Fischer Diskau.
A Singer's Manual of Spanish Lyric Diction - If you wish to dive into Spanish repertoire and already have a working knowledge of IPA, this is an excellent resource to have in your library. If you're looking to purchase it, try eBay and/or check back frequently at this link. The price fluctuates dramatically at different points in the year.
Before linking to my recommendations for basic music anthologies, I want to point out just how valuable a resource that eBay is. I have found countless "out of print" anthologies and pieces of music for incredibly low prices. If you're looking to build your music library on a budget, it would behoove you to look around on eBay, not just for anthologies, but also for the aforementioned books as well. I have marked with an asterisk (*) anthologies I personally feel that all beginning to intermediate students in classical voice should have in their library.
*Twenty-Four Italian Songs and Arias - Available in both Medium High and Medium Low Voice, this is the standard anthology many singers of classical singing typically start out with. You can usually find this in Half-Priced Books stores, eBay, or cheaply on Amazon.
*The Lieder Anthology - Available in both High and Low Voice, this anthology contains 65 songs by 13 composers.
*French Song Anthology - Available in both High and Low Voice, this anthology contains 60 songs by 24 composers.
Anthology of Italian Song of the 17th and 18th Centuries, Book I - Available only in one edition, many of the standard "24 Songs and Arias" can be found within this anthology along with several other beautiful pieces. A great addition to your library for additional Italian pieces beyond the standard 24 most all young singers perform.
Anthology of Italian Song of the 17th and 18th Centuries, Book II - A second edition is available of the previous recommendation. Again, even more great pieces can be found here that fall outside of the standard 24.
*28 Italian Songs and Arias of the 17th and 18th Centuries - There are five versions of this wonderful anthology, however, it may interest you to purchase the spiral-bound edition which contains Low, Medium Low, Medium, Medium High, and High Voice for all 28 songs. For persons looking to build a teaching library, this is essential.