Handy Arduino Uno R3 Pinout Diagram
The original post from Nick Gammon is old, but I’m pretty sure can still be useful.
Check out this handy Arduino R3 pinout diagram and write up from Nick Gammon. He hits a lot of the important points here, and in addition he explains the limits of all the pins and interfaces in the rest of the post. It’s nice to have all this info collected into a single place.