Visual Studio#

Visual Studio Community is a free, feature rich IDE that can be easily installed during Unity's install process.
You can add it as a module through the Unity Hub or install it manually.

JetBrains Rider#

Rider is a paid IDE (free for students, discounts for various groups).
It has advanced Unity integrations that are friendly and helpful for users of all skill levels.
While its Early Access Program is running you can also use it freely.

Visual Studio Code#

VS Code is a free, lightweight version of Visual Studio, but has a longer, finicky setup.