I know there's a lot of free stuff out there to enhance pics taken with
digital cameras, but are there any good ones on which i can view (in real
time) enhancements to the picture whilst moving the various sliders
(brightness, contrast, etc). I know some programs do this, but either the
real time preview is too small to effectively see if you're making the
changes you want, or you have to keep pressing a button 'preview' to see the
changes.

I just want a simple program which will load a .jpeg (not as a thumbnail,
but as a decent size realtime preview), and be able to mess around with the
various sliders and to see a realtime view of how it's changing, then when
i'm happy with the result, be able to save it as a copy (or overwrite).

Cheers
Andy