Unless you've been living under a rock for the last few years, you'll know that the most popular mp3 player in the world by far is Apple's iPod. It comes in all sorts of editions, including the Mini, the Nano, and the Shuffleand every single one is a best-seller.

What you might not have realised, though, is that Apple isn't at all the only game in town when it comes to mp3 players. In fact, they're quite a recent entrant into the market. Companies like iRiver and Creative have been around a lot longer, and their players are usually worth considering too, as they can often be cheaper than the equivalent iPod or have more features.

When you're comparing the prices of mp3 players, the one feature you should look at more than any other is capacity. Don't lose sight of the fact that a 40GB mp3 player can store twice as much as a 20GB one.

However, there other features to look for. Even though everyone calls them mp3 players, mp3s are not the only format you might want your player to be able to playif you want to use it with Microsoft's Media Player, for example, you'll need a player that is also capable of playing wma (Windows Media Audio) format files. If you want to buy music from the iTunes Music Store, you need a player that can play aac (Apple) format files.

Another issue is battery life. Almost all mp3 players are now powered by mains chargers rather than by changing the battery, but battery life varies wildly, from as little as 2 hours up to as high as 10. Make sure you don't get saddled with a player that won't work for a long time if you want to use it for extended periods away from a power outlet.

Of course, the most important feature to many people will always be how their mp3 player looks when they're using and wearing it. There's nothing wrong with that, of course, but don't be fooled into buying a turkey just because it has a pretty design