For graphics cards,
this is still relatively current and has a lot of good information (I'm buying one of the cards recommended here), but depending on when you're actually going to be doing stuff, you may be looking at very different options.
It's also worth noting that
Portal 2 and
Minecraft had PC as their lead development platform, while
Sonic Generations was ported to PC at some point and therefore isn't optimized for the platform the same way those other games would be.
Portal 2 also runs on the Source engine, which has been around for several years now and is still designed to play nice with somewhat older hardware; in my case, I was able to play through
Portal 2 several times on a computer with a single-core processor, whereas most modern PC games require at least a dual-core processor.