For mud turtles, see the mud turtle notes below. For softshells, see the notes on softshells below. Of course, if you pick up a turtle from the road, or a friend drops of a turtle at your house, or you end up with a turtle unexpectedly for some other reason, this question is almost futile. But only almost. If you have been blessed with a turtle, and you decide you cannot fulfill all its needs for whatever reasons, you may want to consider adopting out.
Most herp societies have adoption programs.
And of course, there is rec.pets.herp, where you could post an adoption notice. Turtles are not Ninja Turtles. They will not perform tricks, talk, or perform heroic deeds. They don't eat pizza either. Some turtles like to have their head or shells stroked, but most of them don't like to be held or touched.