As the chart on the left shows, of the 6 most prominent music download distribution sites, it costs the consumer more to buy 10 albums from iTunes than any other site as reported by Ed Bott on ZDNet.
But despite the better deals from other distributors, iTunes still holds a commanding lead in market share, with 69%. That used to be because iTunes had the largest selection, but that's no longer true. According to eMarketer in a January report of this year, iTunes had roughly 11 million tracks in its catalog, Amazon 10 million and Lala offered 8 million (Lala is now owned by Apple). Rhapsody, eMusic, and the Zune Marketplace each have 6 million tracks to choose from.
Even though iTunes holds the lead in market share, that doesn't mean you should discount the other distributors. It's likely that iTunes will continue to lead in the near future, but you may see the others begin to catch up as consumers become aware of their benefits. Cdbaby and Tunecore are still your best bets when planning your distribution campaigns, since it's the easiest way to reach every distributor, both online and with physical goods.
Check out my Big Picture blog for discussion on common music, engineering and production tips and tricks.