TheModernVocalist.com has free video lessons, essays and a vocal technique forum frequented by singing teachers and students. Some content is only accessible to paying subscribers, but a great deal of information on singing exercises, voice science and performance technique is available at no cost.
Voice Council Magazine's website, VoiceCouncil.com, features valuable information on vocal health and training in a number of free articles and videos. Some content on the site is available only to Voice Council subscribers.
Video sites like YouTube host many free video lessons uploaded by voice instructors. A broad assortment of genres and difficulty levels are represented, and some teachers upload playlists of lessons teaching increasingly challenging techniques.