If you want to upload a file with a progress meter you can use mongrel upload http://mongrel.rubyforge.org/docs/upload_progress.html . If you follow the instructions it not that hard to get it running. Though you will be tied into mongrel if you want the progress bar to work.
Other features you may want are Allow multiple file uploads. I dont know of any plugins that allow this. Image resizing, thumbnailing, max image size upload before the image is downloaded. Check the CONTENT_LENGTH in the mongrel handler. image type limitation.
rmagic works well for image manipultion.