A select list of user created nodes
Depending on the purpose of that dropdown, you should have a look at the entity reference module. Here is an excerpt about it from the module's project page:


  Provides a field type that can reference arbitrary entities:
  
  
  A generic entity reference field
  Four widgets:
  
  Two implemented on top of the Options module (Select and Radios/Checkboxes),
  Two autocomplete widgets (one with one text field per entry, one tag-style with comma-separated entries in the same text field)
  
  Two formatters:
  
  A "Label" formatter, with optional link that displays the label of the referenced entity (the node title, the user name, etc.)
  A "Rendered entity" formatter, that renders the references entity using a configurable view mode
  
  Integration with Views (for both forward and backward references)
  Integration with Entity Metadata (and as a consequence with Search API and the like)
  Integration with Devel generate
  Integration with Feeds and Migrate (>= 2.3) for painless data import