Answer 1

gameprogrammingpatterns.com
- great for explaining the modern usage of most OOP design patterns from a, you guessed it, game development point of view. Also has great links to other resources. Expect C/C++ for examples.

w3schools.com
- for most general questions about language specifications, i.e. keywords, functions, syntax, etc.

csstricks.com (if it applies)
- fantastic styling guides and wonderful explanations for almost all of your styling questions and needs

dataorienteddesign.com
- great for breaking down techniques that help to optimize the CPU cache by thinking in terms of data and how the CPU interacts with memory