A quick list of super-useful plugins for Xcode.

Alcatraz

Well, this is essential. Simplifies a lot the install/uninstall passage for almost any other plugin or extension.
Download it by pasting this line into a new terminal window:

curl -fsSL https://raw.githubusercontent.com/supermarin/Alcatraz/deploy/Scripts/install.sh | sh

GitDiff

Highlights every line has changed since the last commit. It is also possible to reset the highlighted lines or just find out what was written there before the editing.

VVDocumenter-Xcode

Keeping your code documented? So annoying without this.
Just enter /// over one of your classes, methods definition, variables to get the Xcode supported documented section.

KSImageNamed

How many times do you forget about the name of that image in xcassets?
With KSImageNamed you get for free a list + preview of the stored images. Just start typing [UIImage imageNamed].

Autoindent with save

If you get annoyed by not having code correctly indented, this is the right plugin to install.
It checks and re-indent all the code every time you press cmd + S.