Assuming that you want to stay within the law (which means paying to receive copyright tracks), here's a list of the top six UK sites, as reviewed by the
Daily Telegraph:
http://www.telegraph.co.uk/technology/3358823/ The-six-best-digital-music-download-sites.html
If you're thinking of getting hold of copyright material for free, you won't find any actual websites offering the tracks. (If they existed they'd immediately be sued, for massive amounts of money, by the copyright owners). All that you'll find are P2P (peer-to-peer) networks and the software that you need to access them. Limewire is by far the most popular software in that category. It's fairly easy to get to grips with but, like all P2P software, it links your computer directly to that of a stranger, increasing the risks of viruses and malware finding their way onto your PC. Additionally, the unauthorised downloading of copyright files is a civil offence, for which you can be sued. Further, P2P networks require you to make tracks on your PC available to others. That counts as unauthorised 'distribution' of copyright materials, which is both a civil offence and a criminal one (which can lead to fines or even imprisonment).
The choice is yours. Stay legal, and use the sites in the link above, or use P2P networks and risk a very big penalty:
http://news.bbc.co.uk/newsbeat/hi/technology/n ewsid_8108000/8108589.stm
Chris