This plugin extends attachments list in Trac.

Drag-and-drop to attach files using HTML5 drag-and-drop, 
XMLHttpRequest Level 2 and File API.
Progress bar while uploading the files using XMLHttpRequest
Level 2.
More than one file for selecting attachment files.
Attach an image from clipboard.
Auto-submit on select a file to attach.

WWW: http://trac-hacks.org/wiki/TracDragDropPlugin