For the Python side of things, which I think is a good language to know for VFX in general (as it's used by Maya, Houdini and Nuke, amongst, I'm sure, others) I generally recommend:
Think Like A Python Programmer. It's not Maya-specific at all, but it's a good introduction to Python as a programming language.
I first learnt MEL (I've not used MEL in a long time, so I've got a bit rusty there!) from MEL Scripting for Maya Animators. It's written for people who aren't necessarily already programmers, so starts from a very basic level. I don't know how recently there was a new addition and, if there's not been anything in a while, how much MEL has changed since it was written, but you might want to look more into it... (The second edition that is shown on the site is certainly newer than the one that I learnt from)