PhpStorm

https://www.jetbrains.com/phpstorm/

Built in support for LESS.

Eclipse

Follow instructions here: http://www.normalesup.org/~simonet/soft/ow/eclipse-less.fr.html

When using this plugin, use @import without the url() notation.
This is still valid:

The Drupal Quickstart virtual machine ships with multiple code editors to edit project files such as PHP, CSS, HTML, and JS (JavaScript). The Eclipse IDE packaged with Quickstart requires some minor configuration to work a little more flawlessly with Git and Drupal projects nicely. Launch Quickstart and Eclipse then follow along.