Nothing gives me the feeling of power like solving my non-programmer friends' problems with a bit of programming.
My girlfriend is an architect, got at her job a task of designing how to cut facade panels. Something nearly impossible to do with her tools and insanely time consuming to do by hand - but it's actually just a subset-sum problem with more steps. After a couple of hours of tweaking the program to properly parse excel files she can export and writing the output in a format usable for her I solved what would be an incredibly tough pickle for her and her whole company.
I'm seriously proud of myself.