Maybe it exists already, but I'd like to see an API for uplaoding files into the Media Library from a plugin and a broswer that would allow you to choose files from the Media Library to be displayed through a plugin. For example, through an audio player plugin, I'd be able to upload the files to the Media Library through the plugin options page and choose those files to appear in the audio player. I'd also have the option of uploading the files directly to the Media Library and, through the plugin options page, hit a "chooser/browser" button that pulls up the Media Library and I can choose which files I want to appear in my player.
Does any of this already exist? I've seen the function wp_handle_upload, but the Codex has extremely little documentation on it, which is pretty frustrating. Does that upload the files to the Media Library or just onto the server itself?