Recording: line-in and microphone

A great feature of some players is the ability to record audio straight to memory. This is great for recording live performances, or for making verbal notes to yourself.

Some devices include built-in microphones, which is far more convenient than something that requires an external one.

Additionally, a line-in jack will allow you to dub from another audio device - be it a PC sound card, CD player, cassette deck or whatever.

PIM features

A few MP3 players have software extras such as text readers, to-do lists, clocks, alarms, calendars, address books and other "personal information management" (PIM) utilities.

An MP3 player with PIM functions may not be a replacement for a PDA, but it is a cheaper alternative if you only want the basics.

Games

In addition to music and radio playback plus PIM features, some players also include some form of game functionality. Two of the best examples of this are Archo's Gmini 400 (with Mophun game support - think newer mobile style games) and the iPod's built in brick and puzzle games.

Equalisers and bass boost

If you want complete control over the sound playback, you'll need an equaliser function. These can range from a simple bass boost to three- or five-band controls right up to presets like rock, jazz, concert hall.

Some players also include audio effects that enable automatic cross fading of tracks (DJ style) and automatic volume leveling (so you don't have to keep adjusting the volume).