Well, when you're just below the smoke point of an oil, it'll shimmer ... but that's only useful if you know what the smoke point for that oil is, and you actually want to use oil for cooking.
I can't remember if it was an episode of Good Eats or on Alton Brown's first book that he recommended that if you had an automatic ice maker, so had consistent sized ice cubes, that you time how long it takes them to melt at different temperatures, so you could use that to judge how hot a grill is.
For grilling, and campfire cooking, I've always gone with the hand near the cooking surface to gauge how hot it is, but I don't know that it's all that accurate ... and people have a different tolerance for pain, so you'd have to do some tests to calibrate. It doesn't work as well for cooking on a stove; I think it requires a more radiant heat source.
For frying, I like the wooden spoon test -- dip something wooden into the fire, and as there's moisture in the wood, you should see small bubbles form if it's hot enough.
... and then there's always just listening as you add food ... try touching down a piece of whatever you're cooking, and if it doesn't sizzle, the pan might not be hot enough yet, if you're attempting to sear it.
If I need warm water for bread, I'll run the hot tap against the inside of m wrist ... once it feels slightly warm, but not hot, it should be good.
None of these are going to be completely precise, but there's lots of ways to gauge temperature other than a thermometer.