Which CPU to buy for Christmas gaming?

For years, one of my own personal holiday traditions has been to take advantage of the cold weather, lack of daylight, and time off by holing up somewhere and playing a computer game. Now that I have a whole new family to visit (post-wedding) and a new set of demands on my time, I won't able to partake of any PC gaming Christmas cheer this year, but if I did I'd need a substantial upgrade.

I suspect that many of you out there are thinking about upgrading this month, and for any number of reasons (e.g., you're a Christmas gamer like me, or you're going to give yourself a nice hardware present, or you have a Christmas bonus burning a hole in your pocket). So for those of you who're planning a major, performance-enhancing upgrade soon, I've put together this short article to get you the lay of the land.

Note that this article is primarily focused on high-end and mid-range processor upgrades, but I'll also mention GPUs, because graphics definitely factors into the bang-per-buck equation.