Just to throw it all somewhere

• Customizeable selected template
• Customizeable list item template
• Keyboard selection (up/down/enter)
• Use left/right arrow keys to move the caret (ibeam) between items (multi-select)
• Filtering list by typing
• Capable of handling rich objects array
• Async data (handled by AngularJS and ng-repeat)
• Pagination (far-future) #316
  • Scroll-based pagination (far-far-future)
• List Groups (future)
• Validation (max/min/etc)
• Tokenization using commas or string-separator (far-far-future)
• Keyboard shortcuts
  • tabable
  • backspace/del to clear the value while closed
  • Key Down to open
• Position
  • Append list to body or any other element #41
  • Collision flip - Show the list above the target (if it dosen't fit) #234

Options(?):

• Close on selection
• Multi-select (tagging) & single-select
• Custom sorting / matching / filtering
• opt-out on Android/iOS devices

This covers almost everything select2 is capable of doing, which is by far the most comprehensive solution currently available.