If you're a Visual Studio web developer and you haven't tried out the Web Essentials extension by Mads Kristensen, then GO NOW, GET IT!
And for those who do know about it, and you were using it for it's LESS support, then you may have noticed in the last update how it was removed :( The only alternative then would appear to have been T4CSS.
But the same day I updated and saw the lack of LESS support, was the same day that I realised it's now baked into Visual Studio in the most recent ASP.NET and Web Tools 2012.2 Update.
It supports adding LESS files from the New Item dialog, and upon build will generate the CSS and minified CSS for it too. Which is obviously the reason it was removed from Web Essentials. Awesome :)