main(p,c){for(p=0;c=~getchar();printf("  %02x"+(p++%16!=8),~c))p%16||printf("\n%08x:"+!p,p);puts("");}

Contributors of shortness to this include:
  Rob Mayoff
  John Dawson
  Britt Yenne

We know about puts("") -> puts(0), but that violates
portability guarantees unless there's some POSIX thing I don't
know about.

Dave Burton points out that p can be declared and initialized more efficiently
if you don't mind a compiler warning:

p;main(c){for(;c=~getchar();printf("  %02x"+(p++%16!=8),~c))p%16||printf("\n%08x:"+!p,p);puts("");}


General rules about the program:
Output must be character-for-character identical with the above program. (No trailing space,
   no extra or missing newlines, no unprintable characters...)
The program must be completely self-contained - no referring to other files for help.
   (standard C things like libc functions are fine)
The program cannot require being exec()ed in a certain way (strings in arg list or environment
   are taboo.)