[fjtorres]

Under those conditions, I think you might want to look at some of the Android tablets, especially the Archos line. Some of the generic asian model will have the virtue of no recognizable branding (if any). There's at least one restaurant I've heard of using iPads for this but you want something less recognizable, I think. It should be about the menu, not the gadget. With Android (or a WinCE-based tablet):

1- They'll be color, larger, and cheaper. Less than US$300, some as big as 10in.
2- you can do animation and audio
3- you could do a streamed menu system via a private web-server instead so the orders go straight to the back room. No need to manually load files or record the order. It shouldn't be hard to find a local website to (relatively) cheaply code you a system. Basically you'd use the tablet as a terminal into your system.

You can do the same with some ebook readers but they'll likely cost more and still be b&w. Battery life will be lower than an eink device but it shoud be enough for an evening of fine dining.

Check the forums around here for suitable webpad/tablet candiates.