File Download plug-in for MobileSafari
This one lets you download most zip and tar files. I tried to make it download png, gif, and jpgs, but because Safari handles it already, I don't think I can ever make that work.
This was developed targeting 1.0.2. I haven't tried it on 1.1.1 or 1.1.2.
(Updated) XianLi says in this thread that it works fine for him on 1.1.2.
No warranty or liability of any kind, of course. Don't blame me if it somehow messes up your data, though it isn't supposed to affect anything outside the Downloads folder it created.
How to use:
Copy the plugin bundle into "/System/Library/Internet Plug-Ins", and then reboot the phone.
It will create a folder called Downloads next to Library and Media in your root home folder. It will only download there.
When you click on a link that is downloadable, a large button will appear. Click on it to download. Click the normal page back button to not download, or to go back when it's complete.
http://www.badongo.com/file/5387192
For more information, visit:
http://www.hackint0sh.org/forum/showthread.php?t=18060

