My first was when my licence was still wet, frayed tail rotor control cables on a Bell 47, you're allowed three frayed cables, there were three left holding. Also found a cooling fan belt holding on by threads. Found an engine oil line untightened after an inspection on a 206, found rags and tools under a 206's cowling more than once, and there was a transmission cap left off. On twins there's engineers taking a good look at the birds prior to us crawling all over them every morning so not much gets missed, although I do know of a 76 thats had the engine cowling flap up into the rotor system while in flight for a missed latch, flashlights flying across the ramp when the heads engaged, and oxygen bottles left on the gear door that planted themselves firmly into someones driveway when the gear were put up through 500 feet.
Timely topic, as discussion has been going around our op of letting the engineers handle the walk-around and pilots just doing the control checks. It probally won't go, while our base engineers are first rate, some of our third world ops don't have the same level of confidence, and it would have to be a company wide SOP.
I rather enjoy climbing up onto the ole girl to have a look before lighting the fires.