Baby's first Quine
I ran into jpo in Bollo's, and he brought up Quines. I've been intersted in Quines for a long time (as a CS person and also, briefly a Philosophy major), but had never written one, and avoided reading any "how-to" information, in anticipation of the day when I could solve the puzzle for myself, and jpo had done the same. We jointly figured out this strategy of having an escaped string containing the code, except for the string itself, and two helper functions: one for double-escaping that string (in my case, stolen from [StackOverflow] (http://stackoverflow.com/questions/3535023/convert-characters-in-a-c-string-to-their-escape-sequences)), and another for inserting one string into another (in this case, just printf).
Anyway, I wrote this monstrosity of a Quine in plain C (jpo had written one using stringify features of the preprocessor before). I'll probably write more and leave them here, because it was fun.
Quinextra
This one is slightly more interesting: you can type in a one-line expression to transform the source code in some way before it gets printed (e.g. reversing it).