Most recently... taking something previous devs had failed at and knocking it out of the park.

Best example was a statistical regression and graphing tool on ASP MVC.

The devs were doing a massive brute force recalculation on the server layer. It would take 24h then fail to save (Entity framework brute force).

We moved it to the database layer and got it down to a passable time.

The same devs were outputting charts to ie 9, chrome, firefox... same deal, half an hour on the initial request (parser churn in the browser)... then failure.

Again got it into a passable time by switching to web sockets and long polling then outputting 1000 or so points at a time to give the browser time to render.

Taking those two cock ups and making them a workable solution was awesome.

Since then, teaching. We have apprentices, newcomers, interns all jumping in and looking to get working. They're all different, what works to teach one person won't the next, each of them so far has caught on to what I was teaching. It's a proud moment to be able to impart knowledge and see someone pick it up, enthusiastically... it's also awesome to see someone excited about what you do.