As for what an artist get from signing with a major label:
http://www.musicbizacademy.com/articles/dl_newmedia.htm
Artist iTunes Royalty (with wholesale markup)
$0.99 download single song price to the consumer
less $0.29 to Apple
left $0.70 x 130% (wholesale markup)
x 12% (net artist net rate) =
$0.1092 cents per download
Artist iTunes Royalty (without wholesale markup)
$0.99 download single song price to the consumer
less $0.29 to Apple
left $0.70 x 12% (net artist net rate) =
$0.084 cents per download
Artists will get anywhere from 8.4% to 10.92% of an Itunes song (if they sign with a major label).
The artist will get 70% if they are their own label (aka they own the rights to their songs)