Take a good, hard look at this list of Unity tutorials by Jasper Flick: http://catlikecoding.com/unity/tutorials/
There are some really interesting tutorials here, and what's more, they're really fun. I can look at the thumbnails for each one and imagine an entire game based on the mechanic they teach.
They're meticulous and methodical, so be prepared to spend a few hours on each one, but, dang will you be glad you did.
They get into fairly complex topics, but don't let that scare you off. I worked my way through Noise and am halfway through Noise Derivatives, and, to be honest, I understood about half of what I was doing. Maybe a little less! But, as I said, they're excellently notated and include project files for multiple steps throughout the process, which is very useful if you can't get something to work quite right.
And besides, if you're trying to improve your coding skills, what better way to do so than pushing yourself out of your comfort zone and ending up with, say, a procedurally generated ocean surface to boot?
If you've still not had enough, take a look at NumberFlow as well. Also by Jasper Flick, this is a free (for non-commercial use) Unity plug-in that does some awesome procedurally generated textures for you in real-time. How cool is that?!