I make it a point to collect any and all garbage I can when diving. Anything heavier than 4kg I put in a bag and lift up with a lift bag. This I think is the most important finds I can make as a diver. Also clean up the beach and leave with more garbage than I came with.
Other than that - recovered some pretty interesting things through my diving career, but I will skip over the "professional finds", some of those are better left for a more serious thread. As for recreational finds:
Several bicycles in working condition.
Weights - about 200 kg overall, including belts with weights
fishing lures, some of those more than 50 years old, obviously hand made!
a set of oil paints (later found out some guy has this "gig" painting oils under water, must have been one of those leaving his "art" behind)
knives - fishing and diving
flashlight
hundreds of golf balls, in the strangest places
an inflatable sex doll, deflated
a rolex watch (still worked, sold it to fix my buddys boat motor)
A purse with a switchblade in it (my favorite)