Hi, I use iViewMediaPro for pictures other than photos imported into iPhoto. I find it useful and easy to use. Just drop a folder of pictures (iViewMediaPro can handle jpegs and most other formats) and a window will open with tabs to see all the pixs or individually. I usually save the catalog into the same folder as the pixs - so I can just double-click it to open instead of dragging-and dropping the same folder into iViewMediaPro all the time.

Update : Was looking for the link to the iViewMediaPro and found out that it has been bought over by M$. Now that's a surprise to me - it was weird looking at the M$ logo on an app which I always thought of as a true-blue Mac app. Anyway, it is still available in Windoze and Mac flavours.

http://www.iview-multimedia.com/mediapro/

I remember using FFView some time ago - it's basically a comic e-book reader. It reads .cbr and .cbz files but should handle a folder of jpegs with no problems. (Quick tip for fellow comic e-book fans : rename your .cbr files to .rar and .cbz to .zip - and unrar or unzip it. You'll get a folder of the comic pages in jpeg format)