WiiSCU by Wack0 (updated by Illinialex24) (mod of IOS51+shop by tona) - powered by PatchMii. The application gives you the option to install new versions of channels and IOSes without touching the system menu.
Remember to be careful with IOS60 if you are on 4.1 or lower, the new version (0.22) fixes the stub issue but it still can be dangerous if your internet or power goes off.
The new version has the source included because of the copyright. The current source download is for v0.21.
Changelog
v0.23 (unofficially contributed by SifJar)
Fixes Shop Channel installation issues by getting v18 instead of just getting latest version