Endnote has a bibtex export style. I'm not sure why they bothered. It doesn't work, it's never worked and from the looks of things this and a couple other issues with Endnote are never going to work. The articles and third party software i've tried just don't work or are a real pain to impliment.
I use JabRef for my bibtex reference manager. They seem to be on top of it. Besides the ease of use and functionality of the software in the first place, they seem to have an easy and built-in (sort of) way to export correctly from Endnote.
In JabRef click Tools-unpack Endnote Filter Set (this is a zip file so put it anywhere)
Open the zip and read the "read me" file. It has instructions to go from Endnote to JabRef and JabRef to Endnote. For our purposes copy BibTeX Export to JabRef.ens and BibTeX Export to JabRef2.ens into the styles folder
(something like C:\Program Files (x86)\EndNote X2\Styles).
In Endnote click on file-export. Then in Output Style, select Use Another Style. In the search box type jab and it'll bring up the two new styles. You can see the difference in the preview pane, but JabRef.ens is the one we want rather than JabRef2.ens.
Save as a text file
rename the file from .txt to .bib and open it in JabRef. You can also import. WARNING!! this will FAIL if any of the references has a bibtex key already that contains a space (or punctuation maybe too). Any key like this needs to be deleted or else it won't work.
In JabRef, select all and click the magic wand to generate new keys for all entries. DONE
I actually exported some references from JabRef an copied all my Endnote exports into that file. There's some stuff in the JabRef export that is commented out. I don't think it needs them, but just incase.