Please see Gmail *2* small attachment icons by Moktoipas and Gmail - attachment icon replacer by USBman for where this came from as it is simply a combination of the two (i.e., borrowed code). The aim was really to update the latter for the new Gmail interface. Whether you use Windows, Mac, or Linux...this should display the attachment icons native to your system. Hopefully it works for you like it does for me!!

EDIT: As someone noted in the comments below, this may not work with the Better Gmail 2 extension for Firefox. I haven't gotten a chance see this problem first-hand, but just note that it may be a problem.

**UPDATE**
This update includes the code from Stybi (see comments section below).