I have found that about any standard-usb kb will work IF plugged into a USB hub that is plugged into the "3G" USB connector in the back. However, they do not seem to "recover" well if the Archos has gone into deep sleep mode, and it needs to be rebooted to get the kb working again. I think I have seen that not all hubs work equally well, so YMMV on that point.
Several different BlueTooth kb's have worked, too (even their touchpads - nice for keeping smears off the screen, although the "mouse" cursor is a bit hard to see on dark backgrounds). And those do reconnect normally even after being turned off, then back on some time later - not sure though about the deep sleep effect noted with the USB kb's above.
This is with the standard 8GB model (aka Staples' "4GB" model with 1Ghz/512MB RAM), with ICS 4.0.3 (Archos FW 4.0.6). I just picked up 2 on clearance for about half the original price after reductions/coupons.