cjbartley, I currently have a 60G and an 80G Apple Ipod for my musical collections that I use both in the car and on the bike. The jury is still out on the "Cycle Sounds" unit because so far I haven't figured out whether the "optional" volume control will give me more control of the volume of the amplifier or if the current setup with the volume being controlled by the Ipod itself is sufficient. Not sure if I want to spend more money to find out.
As for types of MP3 players, my Ipods work fine, but some feel (and so far I haven't experienced this) that because it (the Ipod) is essentially a hard drive that it can be more susceptible to vibration, bumps in the road, etc... that may cause it to freeze or have issues.
For that reason, if you don't have that big of a collection, I would recommend that you get a "flash" drive type MP3 player that should not be susceptible to those issues. Most of them have from 1 to 8 gigs of room to fill up with your favorite tunes and newer models (I haven't really kept up on this end of it because my Ipods haven't let me down...yet) may have an even greater storage capacity.
In any of these you can inset a number of songs in certain types of libraries that you don't have to fiddle much with while riding. As Trirocketman correctly pointed out it can be a hassle to use those "small" buttons. And unlike the sound system you will find on the latest model of the Gold Wing (80 watts per channel X 4 speakers with auto volume and front to rear fader capability plus the input jack for an MP3 player that utilizes the onboard audio system) that volume you set may be awfully loud when you wind your speed down to stop at a red light.
Sadly if you want an ideal audio system get a Gold Wing, the buttons controlling that system are glove friendly and for all the reasons listed in the above paragraph it is the best system on a motorcycle today.
Dennis