I would imagine that approximately 6-10 document types (PDF, DOC, XLS, PPT, JPG, TIF, BMP) constitute 99% of those things attached. Perhaps they could do these in icon form, or put a paperclip icon in there for the other 1%? I’d probably make the column have the icons attached as you would see it in the reference itself - a set of icons (smaller of course) lined up side to side. Like any other column, you can expand it left to right if you tend to have more icons to see more of them.
Besides, many many people like to attach the actual article in PDF form to the reference (this is their library after all!), so knowing if you have a PDF document attached is quite important. Seems like a no-brainer that more information is better than less so you shouldn’t have to open the reference any time you want to see what kind of file is attached(and that a paperclip tells you pretty much nothing)…