I managed to display some comics on a Sony Reader. Only half a page fit one at once. Wasn't terrible, wasn't great.
Comiczeal is as good as you can get with reading comics on the iPhone. (You have to scale the pages to a resolution that doesn't lose any detail, and switch to a different format; .cbz files choke up a low RAM device.) It's not really worth it, you have to flick around so much to read a single page. Nothing short of seeing the full, full resolution page all at once really works for reading comics with electricity.