I use itunes, but yes, there are alot of songs on there that you can't find, so then I'll go to Limewire. It's the only P2P sharing platform that doesn't contain spyware (that I know of).
I highly suggest footing the $18 to buy the Limewire Pro version, you will be amazed at the faster download speeds and how many more items come up in searches.
In fact I'm upgrading to the latest version of itunes so I can buy Justin Timberlake's new CD...just released today!!! WOOT..I'm bringing sexy back.....