Since the thread title doesn't specify a year, I'll leave this tidbit of info here for other 2017 DCers that are looking for the info.
Crutchfield specifies 6.5 for front doors and 5.25 for rear doors (mostly due to clearance, not diameter).
I installed the following with no issues (I did tap the wires before the factory amp and add a 5 channel to drive the new speakers):
Front Doors:
Polk Audio DB6501 6.5-Inch 2-Way Component System (Pair, Silver)
Scosche SAT69 4-Runner Speaker Adapter for 2003 Toyota
Rear Doors:
Polk Audio DB651s Slim-Mount 6.5-Inch Coaxial Speakers (Pair)
Scosche SAT6 Speaker Adapter for 2000-Up Toyota Echo/Avalon
Front Dash: I simply disconnected the OEM speaker, but a nice 3.5 inch would fit there.
Dash Corners:
Mounted the tweeters from the DB6501Cs here:
1. Take an old paint tray, cut it to the shape of the factory mounting plate
2. Use a hole saw to drill a hole for the surface mount bracket of the tweeter
3. covered in Dynamat to cover sharp edges and create a tight fit
