Richard Menta at mp3newswire has been reviewing potential ‘iPod killers’ since 2004 and he rounds up the potential challengers for Apple’s crown in the run up to the Christmas shopping season.

Of the 149 portable MP3 players he has reported on in the past two years, not one has yet managed to dent the popularity of Apple’s device, which has become a generic name for the MP3 player.

The market for portable digital players still contains room for expansion, with only 10% of households possessing one at the moment. This means the opportunity still exists for Apple’s rivals to take their share of the market.

The main potential iPod killer this Christmas is of course Microsoft’s Zune, especially with the size of the advertising budget Microsoft can back it up with.

Microsoft’s MP3 player also boasts a subscription music service and the ability to share music with other Zune users, something that the iPod cannot currently match. Apple boss Steve Jobs doesn’t appear to be too concerned about this new rival though, as he pointed out in a recent interview.

Despite the threat from MS, it is in fact a veteran of the portable music space that might be causing the most concern in Apple Towers… yup, we’re talking about consumer electronics heavyweight Sony.

The Sony PSP is currently the world’s second-best selling digital player, and boasts a bigger screen than the iPod or its other competitors. It combines music, video and gaming in a single device, making it an attractive proposition for people who want more than just music. Sony sells one PSP for every 2.3 iPods shifted by Apple.

And the others? Here’s Richard’s list of potential challengers, some more sensible than others…

Sony NW-S205F and NW-S203F Sports Player
SanDisk Sansa e280 8GB
Sony NW-S706
Samsung YP-K5 MP3 Player has Built-in Speaker
OSIM iGoGo MP3 and…Massage?
Archos 404
Archos 504
Archos 604
StormBlue A9+ Bluetooth
Creative Zen V Plus 8GB
Maxfield MAX-SIN Touch
Creative Zen Neeon 2
NafNaf Hyp resembles Keg-o-beer
Sirius Stiletto 100
Disney Mix Max
Creative Muvo V100
Football Helmet MP3 Player
Acer MP-340
MPIO FL500 Wedge and FY800
Visual Sound VS1
Coby PMP4230
Coby PMP7040
iRiver S10 
Toshiba Gigabeat V Series
Cowon N2 Adds GPS
Wolverine ESP

For a full round up of the pros and cons of these devices take a look at the full list here.