A notice was posted to the Scala mailing list just a short while ago announcing the first release of a plugin for IntelliJ IDEA.
You can see a high-res screenshot of it in action or download it.
As Eugene Vigdorchik wrote in his message, here are some of the features in the plugin:
The feature highlights are as follows: syntax highlighting, formatting, parsing errors highlighting, folding, surround with, file
structure outline, keyword completion, goto class, compilation (with no dependent files calculation yet), debugging, cross-language resolve of types/find usages/rename of classes and traits.
Definitely looks very cool. Martin Fowler? Bruce Eckel? Bruce Tate? Dave Thomas? Are you guys listening?