$/
  artifacts/
  build/
  docs/
  lib/
  packages/
  samples/
  src/
  tests/
  .editorconfig
  .gitignore
  .gitattributes
  build.cmd
  build.sh
  LICENSE
  NuGet.Config
  README.md
  {solution}.sln

• src - Main projects (the product code)
• tests - Test projects
• docs - Documentation stuff, markdown files, help files etc.
• samples (optional) - Sample projects
• lib - Things that can NEVER exist in a nuget package
• artifacts - Build outputs go here. Doing a build.cmd/build.sh generates artifacts here (nupkgs, dlls, pdbs, etc.)
• packages - NuGet packages
• build - Build customizations (custom msbuild files/psake/fake/albacore/etc) scripts
• build.cmd - Bootstrap the build for windows
• build.sh - Bootstrap the build for *nix
• global.json - ASP.NET vNext only

.gitignore

[Oo]bj/
[Bb]in/
.nuget/
_ReSharper.*
packages/
artifacts/
*.user
*.suo
*.userprefs
*DS_Store
*.sln.ide

There's probably more things that go in the ignore file.

• Update: Added docs folder
• Added README.md and LICENSE - Critical if you're OSS, if not ignore it
• Renamed test to tests
• Added lib for things that CANNOT exist in nuget packages
• Removed NuGet.config for people using packet :)
• Added global.json for ASP.NET vnext
• Added .editorconfig file in the root (x-plat IDE settings)
• Added NuGet.config back because people were confused about it missing