Try to get used to pressing S when you want to stop moving. It'll stop all movement and auto-attacking, so you don't have to keep clicking around.
Olaf is kind of a champion you have to be really "quick" about. You need to do stuff fast with him to bring out his full potential.
I can't think of many champions. There's Jayce who switches between melee and ranged, for when you need to safely farm from a distance, and when you need to get close and bring the pain.
Sorry, simple top champions isn't my area of expertise. I'm sure someone else will help with that though.
EDIT: Yes, Garen is pretty simple. He's kind of susceptible to ranged poke though, but he's fairly tanky and does decent damage.