These are the most hearted Pens of 2015. Quite impressive! http://codepen.io/2015/popular/pens/. If you are a front-end developer, I would recommend you to set some time aside to review all these examples. They give a real taste of what's trending at the moment and the kind of stuff that the browsers support nowadays.
I can see there's a lot of material design look and feel experiments going on, which confirms the UI design buzz that we've been hearing last year.
Among all these great examples, I specially liked the animated curved content. Mostly because we built something similar (without the animation) for the Dove project and maybe this animation would have looked great on it.
These navigation animations examples are not very impressive but can be quite useful for small websites or microsites:
Another trend that we have seen in the latest years is the animated hamburguer menu icons... Well, now look at this animated search input icon/field and don't tell me it doesn't look sexy!