There are a plethora of choices for electronic citation applications.  Perhaps the key features that best represent a good referencing application are inherently the same criteria for good software in general, such as:

1. stability
2. accessibility (i.e., cross-platform, cross-application)
3. supported
4. accurate (generate correct formats)
5. user-friendly

An application that is very close to meeting the aforementioned criteria is 'Zotero'.  In addition, Zotero is open-source and free.

There are a few quirks with the Zotero application that are useful to remember, such as:

• The Firefox version is separate from the stand-alone application (i.e., you would need to export/import collection)
• 'Removing' the selected item does not delete the reference from the library.
• Adding a PDF link from a webpage may require manual entry of further Info (i.e., 'Save Link as Zotero item' results in a PDF with a link)

Zotero is the most versatile citation application that I have found, that is universal, free, and just works.  This app would be my first choice for OS X or Windows.

Reference Links:

1. http://en.wikipedia.org/wiki/Comparison_of_reference_management_software
   (a good list but not complete - missing Procite, Citation 9)
   
   
2. http://help.libreoffice.org/Writer/Creating_a_Bibliography
   (LibreOffice bibliography via database component... similar to MS Office... but free)
   
   
3. http://www.citationonline.net
   (commercial Citation 9 for Windows)
   
   
4. http://www.adeptscience.co.uk/products/refman/reference/chart.html
   (Comparison of EndNote, Reference Manager, ProCite)
   
   
5. http://www.burioni.it/forum/dellorso/bms/text/index.html
   (Personal Bibliography Management Software - a bit dated but interesting to compare with item #1)