Good/inexpensive site to download for MP3 portable

I just got my son an MP3 player for the holidays. (must be politically correct here)

I know about Napster, but that can be a little pricey for an 11 year old.

Are there good sites for him to get the music MP3 downloads that will work well on his MP3 portable?

I will be also very interested to find out how the sound is through my big system, but the real purpose is for his portable.

Thanks for any info.

iTunes 99 cents a song. has a subscription model that's $10 a month and frees you from the worry of going over a budget. does NOT look like a site for 11-year olds...LOL!