Here's where to find Wii, GameCube, and older Nintendo ROMs:
This site has an extensive collection of ROMs for almost every console, including Nintendo Wii. You can search and filter by genre and region3.
This is another free website for downloading Wii ROMs, where you can sort by popularity or alphabetically. It includes user ratings and information about the ROMs3.
This site offers a variety of Wii ISO download links, including both famous and less popular games. You can filter ROMs based on region and number of downloads3.
This website lists both regular and most-downloaded Nintendo Wii ROMs3.
This site provides details such as the name, category, rating, size, and download rate for each game3.
This site is another source for Wii ROMs1. Note that Vimm's Lair has removed some games from its archive due to requests from Nintendo, Sega, and Lego4.
This site offers Wii ROMs in ISO, Nkit, and WBFS formats for emulators5.
Ghostware has uploaded a Wii Rom Set to Archive.org1.
It may be useful to use a tool such as Wii Backup Manager to add games to your hard drive2.
The GameCube Vault contains every known GameCube disc, synchronized nightly with Redump6. All downloads are in .7z format and can be opened with 7-Zip. All games are in .ciso and .rvz format built with NKit 26.
The search results do not list alternative locations for NES, SNES, and N64 ROMs.