Learning by samples:

  1. Google Code Search
  2. Krugle
  3. Byte My Code
  4. Dzone Snippets
  5. Code Fetch
  6. Codase
  7. Snipplr
  8. O’reilly Code Search
  9. JSourcery
  10. Merobase
  11. GitHub
  12. Koders

Credit: 10 Code Search Engines