All previous advice is spot on and it comes down to your preference. But one thing that I would suggest is that you make sure that it is flash-based, rather than hard drive. Hard drives don't handle vibration very well or very long (just in case you have that rare bike that vibrates). If someone already mentioned this, I apologize...

 

I bought a MP3, 8gig at walmart.com for $50 it is easy just drag and drop the songs. I pods were more money.

 

I have a Zune and prefer it to the Ipod. The Itunes program is alot more difficult to operate than Zune. I dont have to convert the files or anything. The only downside to the Zune is that Ipod has alot more accessories for them and you have to kinda look for Zune stuff.

 

I use a sansa fuze, 4 gb memory. 72 bucks at walmart holds 1000 tunes. Heres a pic mounted on bike.

 

As others have stated the 2nd generation Ipod Shuffle is the easiest and best that I have found. It can handle the vibration from the bike while other Ipods can freeze up if you mount them to the handlebars and they get alot of vibration. I plug in my shuffle and clip it to a bandana on my handlebars.

 

I just had to chime in here as I knew most were going to say I stink'n pod... I prefer the Sony Walkman, I have the 8G, plug in to your pc and it acts just like another file system drive. Drag/drop. No extra software required. It will play MP3, WMA, WMV2, AAC-LC3, PCM, & MP4... the I pod does not. Great battery life, you can watch movies on it, and it has an FM radio. You can carry pics on it and files if you want to also. all for about 100.00. I have the 1st generation of it when they 1st came out (about 3 years ago) and have not had 1 single issue with it. Trust me when I say you have alot more music options with this non restricted music file system.

 

I've had a ton of MP3 players of all kinds, and It's pretty hard to beat ipod. Easy to manage, and easy to import songs from your CD's. Also Easy to burn 150 song MP3 CD's that play in your bikes stereo.

One word of note tho, I've ruined a total of 3 Ipods on my bike. The bigger ones with the hard drives (Ipod Classic) don't take vibration over long periods of time. Plus they can tend to lock up. The Nano's and the shuffles don't have a hard drive, and so they last a lot longer on a battery and theres no moving parts inside them to rattle apart.

Plus the nano's are smaller.

 

Sounds like the iPod Shuffle is what you're looking for. The 2g retails for $80 or so at BestBuy but is probably cheaper on eBay. It's also the smallest Mp3 I've seen. Just my opinion though.