Music downloads - Help!

I need help! Now that I have a computer that isn't a dinosaur, I want to start downloading music again. However, I want to do it legally and actually pay for the songs. Ideally, I'd like to use something where I can choose and buy songs/mp3s individually. I've heard iTunes comes in some odd format that can be converted to regular mp3s, but I'd like to make things as simple as possible. Napster charges a monthly fee for unlimited dls, but it seems that I can't keep the music if I cancel my subscription.

What do you all use, if anything?