Our GM puts small magnetic squares on the bottom of our minis to make using the markers easier.
We do:
red = bloodied
gray = slowed
dark gray = immobilized
black = restrained
green = poisoned
orange = on fire
light blue = dazed
dark blue = stunned
Spare colors are used by defenders to mark. I don't other conditions have come up often enough for us to have a consistent style.
In one combat, when the room was pitch black and we weren't sure what we were fighting, the GM just used the markers to represent where we heard the monsters, instead of using actual minis. I thought that was kinda cool, especially when in the middle of combat, a 2-inch (large) disk showed up at the edge of the battlefield and began to tromp toward us.
I plan to do something similar in a game I'll run next week. The group will be in the cavern tomb of an elder, sleeping god. His slumber is disturbed by any sort of light, causing those caught in bright light at the start of their turns to take psychic damage that ramps up by an additional 5 for each turn you stay in the light. I plan to keep white tokens handy to make it clear who has bright light sources, and yellow for dim light sources.
(Part of the trick to the combat will be keeping the dragon who lives there in light. The multiple PCs can take turns having light sources, just getting pinged for 5 damage, whereas if they can keep the dragon illuminated, he might end up taking 20 or 30 damage in a round.)
The silliest we ever got was a beholder that was dazed, marked by a paladin, weakened, taking ongoing disintegration damage, ongoing bleeding damage, and was either slowed or restrained or whatever it is that Evard's Black Tentacles does these days.