Here the list of sites I've found useful. You can contact me if you want to add your own site here.
NOTE: I accept only quality resources!
mp3, video schools, e-books.
Useful sites that includes articles, tips, lessons and other information related to singing, music business and music in general.
Record labels, accepting demos or not.
Directories, magazines & e-zines and other useful music resources.
Personal singers' homepages.
Personal sites of songwriters.