I am looking to purchase an MP3 player (not having owned one before), and have been unsuccessful finding any information on some of the functionality I would like in a player.

*I need a player that will function on wall adapter or battery power. The majority of the time I would be using it would be at a desk with power outlets, and I'd like to be able to use the adapter for playback capability, not just for charging the batteries.
*Swappable (as opposed to integrated) batteries are a plus. If there are no MP3 players that allow you to use them only from wall power, then swappable batteries would be a requirement.
*I'm in the US, so it must be a player available in this country.
*Preferably 20+ GB storage.
*Besides MP3, WMA and OGG playback would be a bonus (but not required)
*Video playback is not necessary, nor does it exclude me from purchasing a player.
*A current model or still selling model that is still supported by the manufacturer.

In short, I'm not looking for anything too particular, outside of the power source during playback. Wall outlet playback or at the minimum swappable batteries are a must. Unfortunately, every review and online user manual I've read/browsed has not specified the usage of the AC adapters available with the players, but the impression is that at least many MP3 players' adapters are for charging only.

I'm looking for an MP3 player instead of a CD/minidisk player as I will not be able to carry media disks around with me. Is there a player fits this description?

All hard drive based Digital Audio Players (DAP) or Portable Media Players (PMP) runs off of rechargeable lithium ion batteries and most will not be user replaceable or removable (at least not easily and w/o breaking the warranty). HDD based players are relatively power hungry. If you want to connect the player to the A/C outlet then you have no choice but to do so with the battery attached.

Only flash based players will have a removable battery, but they are limited to 2GB of capacity. You may find a 4GB version if you look hard enough.

Life is full of compromises.

Go to frys, compusa, etc.

Why are you asking this here?

Flash players are not limeted to 4gb.... the 16gb Sandisk sansa view is coming out in around a week or 2 and you can preorder it a jr.com for $200 and 8gb micro sd cards are comin out in somtime this month so you would be set. they have 4gig micro sd cards now.