WiX toolset v3.5 is now officially declared Production/Stable. The final build number is 3.5.2519.0. You can download it from here.
WiX v3.5 delivers official support for Visual Studio 2010 and IIS7. The standard UI also supports a quite few more languages (but not all of those) and we simplified the WiX language a bit. Plus there are a bunch of bug fixes in WiX v3.5 that makes this release the best version of the core WiX toolset ever released.