I find myself using Dolphin a lot since it is often easier for me to access than my GameCube or Wii, and it is good for research. To keep my games a bit more organized and easy for me to navigate, I decided to make some simple folder icons. I mostly use Dolphin for GameCube games, so I made icons for all of my GameCube game folders (I generally keep extracted ISOs in the folder of the game it came from). I also have a few Wii and Triforce.
They are very simple to make since Dolphin can export any game's banner. Just resize it to 512x171 without any interpolation and just stick it over any other banner. A GIMP Project file is included for anyone who uses GIMP. I have made almost one hundred, so that should be a great start for most Dolphin libraries.
Update: I have added more icons! Every GameCube demo disc known to exist has a dumped icon (if available). There are also a few more games overall.
Folder Organization Tip: I organize all of my ISOs in their own folder - kind of like a case for the game and the disc is inside! To keep them in a logical order, each folder is named like this:
Template: SYSTEM - Game Title (REGION - 2 Letters) Version Number if Applicable
Example: GCN - Super Smash Bros. Melee (US) v1.2