CDISPLAAAAAY!

Oh My God, I love this program.

I simply cannot imagine life without it. If even one of you poor bastards isn't using it...
Simple-assed thing. Opens any .rar or .zip file, displays all the images within. Rename the files to .cbr or .cbz, CDisplay opens them on it's own and gives them a cool little icon. Japanese mode for these crazy backwards-reading books. Decent colour correction came in handy a few times. I have my mouse buttons set to fit, fit width, original size, open files, fullscreen toggle.
On fit or fit width, blows up my new zzinserted.gif all oppressively fullscreen without me having to be such a dick to make it that big in the first place (this was completely unforeseen but I love it).

It's not perfect. Doesn't open .7z files, won't animate gifs, and sometimes the zooming gets a little wonky. Hasn't been updated since 2004. I've tried newer programs but none of them have replaced CDisplay in my heart.

God bless you, David Ayton.