® (registered trademark symbol) - ALT+CTRL+R
¢ (cent symbol) - bit more tricky, hold CTRL and press /, then press c whilst still holding CTRL!
° (degree symbol) - hold CTRL and press @, then press space
By the way, these can depend on what keyboard you have - mine is not an English one, so to get @ I have to press shift too!
But we still haven't got onto those symbols that are inserted with ALT+xxxx (a four digit number) - we'll leave that for next time!