Is there a plugin that lets you specify which images to crop to a thumbnail?

I’m looking for this:

A way to create a few additional thumbnail crop sizes, that will only be used on *some* images – for example, a homepage slider, an image size that I don’t want ALL of my uploaded images to crop to.

Ideally: go to the media manager, select the image, select the (predefined) thumbnail size I’d like to crop it to, generate that new size for that image only.

I could have sworn I found a plugin that did this last year, but can’t seem to find it now.

It would be also very nice to have a visual crop tool that lets you set the position of the crop (as opposed to WP’s default center cropping)

Any ideas would be greatly appreciated!