If you are looking for a very compact case, the Ruger "Scoped Rifle Takedown Case" (the same case that comes with the Ruger 10/22 Charger) fits a broken down (barrel removed) non-scoped AUG perfectly. It is well-padded, and has lots of velcro patches to secure everything down, and the top zippered pockets will hold at least three 30-round mags. At 24" long by 10" deep, it is about as compact as it can be and still fit. At $80 its a fair price too. Available in Ruger's online store. I've got my AUG in one right now... I'll try to post a pic of it fitted in there later.
Once I have a scope, I do really like the Mojo Explorer
pictured a few posts up -- might have to source one of those!