After the storm of controversy I caused with my preference for two-hole punched paper, I'm sticking with a safe one.
Pandora Radio is a website where you type in songs that you like, and it finds other music that is similar to that song. You can then 'like' or 'dislike' songs and add secondary songs or artists to refine it. And if you find something really good, you can then buy it on i-tunes or download it from limewire, depending on your inclination. Cough. So it's not only a great way to get music to suit your mood on various occasions, it's also a great way to discover new artists/songs. This is particularly good when your hard drive dies the day before you copy everything onto an external one and you lose all your music. The only thing I don't like about it is that it doesn't have songs that weren't released in the US on it, so it's a little thinner than I would like on British music*.
Tragically, you can't get it in the UK. Anyone want to work out the business model and find a way of getting it in Europe?
* if you're interested, the way I worked this out was by searching for Chesney (for Americans, there's a video of Chesney's 'one and only' hit here). Yes, I'm sad. Live with it.