I'd recommend a self-encrypting hard drive (SED). Not perfect, but they do work, and they don't slow down your system, except for bootup (assuming you are putting the decryption key in the pre-OS-boot sequence). These are becoming more mainstream in business/enterprise and widely available (Dell sells them as part of a system package, now, e.g.). Here's a vendor page with some info : Western Ditgal/HGST Self-Encrypting Drives.