IO::All stands out in my opinion. It seperates All.pod from All.pm (which I have always felt is the right thing to do), the comments stand out and make sense, the coding style is kept clean and consistent (something sadly lacking in many otherwise good modules).

I haven't looked at the code for Brian's other modules (such as Inline, Kwiki and YAML, to name a few), but I assume they are also excellent examples of Perl code, having been written by the same person.