There are tonnes of resources you can use to sharpen your skills or learn new stuff. Some of the ones I'm using now, or have recently used are listed below.

Polyglottal

Cracking the coding interview

Hired in tech has some awesome resources for algorithms, white boarding, and more.

JavaScript

Frontend masters has some seriously cool training resources. Especially the one week course:

Jabber is the JavaScript podcasts for devchat (see above).

Node

Unix

HTML

Heroku

Neo4j

Regex