Either the case or keyboard. Both from the mid 80's. Still finishing up the monitor which uses an iPad 3 display with an adapter to displayport. Have had this case through three different builds, starting with an i7 930, and now currently with an i7 4930k. The case was originally from a broken IBM 5150.
Coming from a G2, I wish I waited for the G3 because of the replaceable back, my favorite feature. My galaxy nexus's battery failed after a while and needed to be replaced, something my G2 cannot do, but the G3 can.