In no frackin' particular order.
- Apache mod alias "Redirect" feature. Smashingly shiny! Saved my butt because tiny_mce somehow ain't doing relative url mapping.
- JPEGImageEncode/Decoder and JPEGCodec bundled with most JDK's. Automatic server side image resizing galore. No more excuses to not accept high resolution images.
- The lazy web, for providing algorithms to keep that frackin' image aspect ratio.
Some thoughts, making an application user friendly is like asking a makeup artist to make her model look natural. Its a long and not so easy process.
-- drag and drop, resize on demand, server side processing junkie...