My keyring is a caribiner (for no particular reason other than it's bright purple and easy to spot) with my car key, bike key, and house key on it.
When I was in high school I had a thermometer keyring like this:
It's meant to go on your zipper but I always used it as my keyring as I only had a house key.
Next time I'm home I should take a picture of my dad's keyring. Holy crap it's huge, and it keeps growing. My dad's a high school principal, and on top of all the keys for his school, he keeps all our car keys (4) on there, house key, PO box key, etc. His keyring has always been enormous, and he's super-protective of it. He keeps a seperate keyring handy at all times in case he needs to loan one of us a car key just so he won't have to give us all his keys.