I use a portable dvd player case from Circuit City.
Unfortunately it appears it is their own brand, so nowhere else will have it.
http://www.circuitcity.com/ssm/Verge-Po ... tDetail.do
It fits inside of the main compartment really well and has plenty of storage areas for accessories (a mini mouse and power brick are all i carry so far, but more will fit). The second picture shows it from the other side, which allows you to see that it is really just a mini laptop bag. I got mine for $25.99 in the store.
Inside, there are slots to hold cds in paper slip cases and a strap to hold the device in place with. It also has a headphone splitter built into it (a feature that I do not want, but oh well). When I put the AAO in this case, I use the slip case that it came with as well to avoid scratches from the headphone jack and the D loops that are inside (they are used to mount the case to the back of a car seat, after all it is a portable dvd player case).
Also there are straps to keep the lid from opening too far; I think i am going to cut them off.
Hope this helps some people looking to transport their AAO.
-Syco54645
ps. for a smaller one that the AAO barely fits in, try this
http://www.circuitcity.com/ssm/Case-Log ... tDetail.do
I wanted protection as well, so I went for the slightly larger one.
edit: I guess I will attach a photo of it from the site