How to identify and fix images with large file sizes?

We have built up a nice WP site, but I am getting nervous about the images. We have not been consistent in the way to use / prepare them as our site has grown, and I think we now probably have quite a few unnecessarily large items, slowing the site down. (Large in bytes not pixels).

So, my question!
Is there a way to sort by size in the media library? If we could look at the biggest offenders we could probably get most of the benefit for not much work.

Alternatively, any plugins that can be trusted to do a decent job?

Thanks,
Nick