APL? I had a friend (who was involved in building the engine monitoring software for the Rutan Voyager) described APL as a "write-once" language.

I don't think coding for readability and coding for maintainability are that much different. In either case, the program has to be written for an audience, and the chances are the audience will be less skilled. This may mean eschewing perfectly valid Perl, such as multiple statements on one line, or leaving in syntactically meaningless white space, or (horror!) putting in use English;, or adding parentheses that are not strictly needed.

I tend not to be too fussy about indentation (as long as it's reasonably consistent: 2, 4, 3, whatever is fine). I tend to dislike the practice of splitting long lines before operators, e.g.

$x =  $a
+$b
+$c;
[download]

with "operator" including both arithmetic and logical operators.

I tend to keep my copy of Kernighan & Plauger's The Elements of Programming Style near to hand. Despite the examples being mostly in PL/1 and FORTRAN-66 (pdf file), most of the basic concepts are still applicable.

Probably the most extreme version of "readable code" is Donald Knuth's Literate Programming. I've never tried it (has anybody here tried it?)