Is there any IDE with syntax highlight support for LESS?
Eclipse does not support .less fully (nested rules, single line comments, etc) but you can at least configure it so that it would open .less files and treat them as .css.
Preferences > General > Content Types: find "CSS" entry and add .less extension.
Then, Preferences > General > Editors > File Assoc: add .less extension and associate with CSS editor.
Better than nothing, especially if you're into Eclipse world ;)