Plugins - Attachment Fu
Add to favoritesattachment_fu is a plugin by Rick Olson (aka technoweenie) and is the successor to acts_as_attachment. To get a basic run-through of its capabilities, check out Mike Clark’s tutorial http://clarkware.com/cgi/blosxom/2007/02/24#FileUploadFu.


If you want more than one attachment per model check out the file_column plugin. It doesn't have S3 support but it allows you to treat a file as just another column type in your database.
I was unable to get the Amazon S3 backend to work properly (in Rails 2).
Note: Only allows 1 attachment per model (as of june 2007). I'm 'bout to hack myself an attachment_fufu...
What's the motivation behind the re-write?