As RM suggested, we can compile a list of candidate questions which might be worth migrating.  Please edit this answer and add more posts.

Candidates for migrating from SO
--------------------------------

 * [What is in your Mathematica tool bag?][1]
 * [The clearest way to represent Mathematica's evaluation sequence][2]
 * [Minimal effort method for integrating C++ functions into Mathematica][3]
 * [Best practices in error reporting (Mathematica)][4]
 * [What are the benefits of switching from Rule and /. to OptionsPattern[] and OptionValue in a large application?][5]

  [1]: http://stackoverflow.com/questions/4198961/what-is-in-your-mathematica-tool-bag
  [2]: http://stackoverflow.com/questions/5459735/the-clearest-way-to-represent-mathematicas-evaluation-sequence
  [3]: http://stackoverflow.com/questions/8140869/minimal-effort-method-for-integrating-c-functions-into-mathematica
  [4]: http://stackoverflow.com/q/6560116/421225
  [5]: http://stackoverflow.com/q/6617511/758485