I found an excellent blog post by Trail of Bits that helps to explain some of the details of Meltdown and Spectre.
https://blog.trailofbits.com/2018/01/30/an-accessible-overview-of-meltdown-and-spectre-part-1/
It is especially useful when combined with a good explanation of branch prediction from Stack Overflow:
https://stackoverflow.com/a/11227902/2555197
I will link the other parts as they are published.
