I've heard of people having several "head shims" made in different thickness’. The head and often the block are milled down quite a bit. Depending on whatever suits their current mood, a shim will be selected and placed between two head gaskets. It's useful for testing different engine setups, but a lot of screwing around.
Saab has a neat variable compression engine that they've been tinkering around with for the last few years. It physically moves the crankshaft closer or further from the head to vary the ratio from 8:1 to 14:1. The motor is 1.59 liters and can produce 225 HP and 224 lb-ft of torque. That's 150 HP per liter! It can do that because it has a supercharger that pumps out 40 PSI when needed. I think the purpose of this experiment is to crank out big ponies and still get great economy by using the high compression ratios. Turbochargers are still probably a superior system, but lack the novelty.
These can be fun to play with:
http://www.bgsoflex.com/crchange.html
http://www.wallaceracing.com/calc-crchg.php
...If only we were starting with a
reeeally low compression ratio.