Wireless keyboards run the inherent risk of exposing their data due to the relatively broad transmission range, and the ease with which highly sensitive receivers (remember, making an RF signal audible is more the job of the receiver than the sender) can be built.
Recent studies have also shown that even wired keyboards can be exploited via the RF emanated along their cable.
Even beyond RF sniffing, there's always the risk that some "cleaning lady" might throw on a hardware keylogger between the keyboard cable and the PC.
Are there any keyboards that are secured (via encryption, shielding, and/or other means) against monitoring via electronic signal leakage or interception?
EDIT: I suppose I should be clear, in that I'm only looking to see if there are keyboards designed to prevent interception or monitoring of their electronic signals. Please do not address any other attack vectors in answering this question, except perhaps as a sidenote. I am aware that these attacks still exist, but the measures available to defend against them are beyond the scope of this query.