If you search the web for Excel resources, it's often overwhelming (/frustrating) to navigate the slew of results that come back. "133 Excel Tutorials!" "50 Excel Shortcuts!"
In my ongoing quest to develop great Excel workbooks, here are the sites I seem to end up at again and again.
The tag line pretty much says it all: Become Awesome at Excel.
It's almost inevitable that you'll end up here if you're trying to figure out Excel charts.
A blog with some great excel tips. I tend to scroll through and think..."I want to know that!...and that!...and that!" It's click baiting for nerds.
When you've Googled the heck out of your problem to no avail, head to these two StackExchange sites. Users collaborate to ask and answer questions, and literally thousands of Excel (SuperUser) and Excel VBA (StackOverflow) questions are archived here.
A great index of topics -- a fun way to figure out how just how much you don't know about Excel.
If you know of a great Excel resource that's not listed above, add it to the comments!