Here's a schematic of the prime number calculator I'm working on. Last night I finished wiring all 12 shift registers for the primary display, so now it's time to start working on software. Notice that we have a lot of pins free still. This will be advantageous if I decide to go crazy adding extraneous functionality, such as fancy displays (LCD?, 7-segment LEDs?, VFD?, all 3?!) or creative input systems (how about a numerical keypad?).
After feeling the stink of paying almost $15 for 100' of yellow, 24 gauge, solid-core wire from DigiKey I was relieved (and a little embarrassed) to find I could score 1,000' of yellow, 24 gauge, threaded wire for $10 at Skycraft! Anyway, here's the current schematic.