The Release Candidate of .NET 4.5 was released today together with Visual Studio 2012 Release Candidate (working name VS11), Team Foundation Server 2012 Release Candidate and a brand new Windows 8 Release Preview.
You can download .NET 4.5, Visual Studio 2012 as well as TFS 2012 here.
You can download the Windows 8 Release Preview here
Note that you may also download all those versions from MSDN if you have a subscription.
For more information on what’s new in the RC of Visual Studio when comparing to the beta you can read Jason Zander’s blog post.
If you want to evaluate all the new features and test the new versions you should quickly download and install them in a testing environment. Remember however that you should not use them in any production environment since the final versions still could change and since you won’t get any support for Release Candidates.