Wii

The Nintendo Wii is arguably one of the easiest consoles to run Homebrew on. There are several exploits currently available, some of which require nothing but an SD card and an internet connection to pull off.

Currently working exploits include;

Letterbomb

Smash Stack

Indiana Pwns

There are ways of running backup games on the system through software, and hardware. The most notable way of running backup games, is through a USB Loader, however, you will have to use google for that.

Resources
http://wiibrew.org

http://hackmii.com