Has anyone ever found anything valuable with a metal detector. And where are some good places to go detecting?

Answer 1

Go to the beaches! People lose jewelry and money in the sand all the time.

Answer 2

Found gold nuggetts just today :)
for relic hunting though, check parks, schools, venues, places where people picnic, have family gatherings, or get together in large groups for whatever reason.
Have Fun!

Answer 3

Old unoccupied buildings; homes, schools, business places. Ask permission first. Check around doors and parking lots.
Also check gardens, parks.