I know a site to download mp3s.
Try
www.allofmp3.com
It's a Russian site, but you can select the English version. Strictly speaking it's neither legal nor illegal. Because the site is Russian, they pay royalties to artists at local rates ie not a lot. Which means, the major record labels don't get anything! It's like 'grey imports' on the net - Buying something cheaper from another Country.
*It's not P2P, like limewire etc, you have to pay for the songs*
You can download in various formats, mp3, AAC, OGG etc, and select at what bitrate you'd like to download, from 128kbps to 320kbps. Or even the original CD codec/bitrate.
You can download an album for around US$2. This would depend on what bitrate you've selected, as you're paying for file size, not per song. They have a big catalogue, and all of the latest stuff.
*I'm merely telling you about this site. I myself read about it in PC Pro magazine, in the UK. It's up to you to decide if you want to buy songs from this site*