That sounds like some cool mods, be sure to post a pic. Now onto mine as you asked:
Well, my first mod was cutting up a Dell server case to fix a different mobo, and rewiring the front panel from the small floppy/ide style connector to the sort used on most mobos.
It was because of the uber l337 fan ducting system and it let me get the Athlon 650 up to 1400mhz, which I was quite impressed with. (even though I only got that speed by accident as I soldered the resistors wrong, but it ran stable, so I was happy

)
Other than that, I attempted modding a Commadore PC-III case to take an AT mobo and PSU, but I messed up and snapped the mobo getting it in, and ended up making a keyring out of the 387 chip, and put the 386 out of the board in another machine.
Last one: I put a window in the side of my current case, nothing fancy.