By genre...
• PnP: Dungeons and Dragons
I'm shocked and awed that nobody has mentioned a single non-electronic game so far. Anyway, your mileage may vary, depending on your dungeon master and the edition of the rules you use, but when a week of eyestrain has caught up with you, and you want to keep gaming, a session of D&D is just what the doctor called for.
• Board Game: Risk
I got my father's 1980 version of the game (yep, four years older than me) as a bit of a hand-me-down, and I can still play it for hours with a few friends. I'm not sure any video game has really conveyed the same feeling of the world's fate hinging on result of a handful of die rolls.
• Cards: n/a
It's been a long while since I gave up playing TCGs, since my budget couldn't support such a habit. For the same reason, I really don't do too much gambling, otherwise I'd probably be playing poker every weekend. Just throwing the catagory out there to inspire others.
• Minis: n/a
Again, just throwing the catagory out there for others to consider.
Maybe I should hit the video games now, before someone mistakes me for being Amish and rallys a lynch mob...
• FPS: Descent series
Pick one of them. I like it. Between the Descent series, FreeSpace 2, and the MechWarrior series, I've worn out four joysticks. Two of them broke when I played Descent exclusively. This is one of two or three games that I continually come back to, regardless of what else I've been playing.
• RTS: Black and White
I really don't like the traditional RTS. I mean, I
really don't like the traditional RTS. "I build 1000 tanks (or Zerglings) for the win," pisses me the hell off. You can't very well make a game that rewards such silliness, while calling it a strategy game. Black and White, while not perfect, takes an entirely different approach to the genre, taking away some of the player's control over production and such, while giving the units a bit of free will. There's certainly more depth of gameplay in Black and White than every traditional RTS I've played, combined. I'm anxiously awaiting the sequel.
• Turn-Based Strategy: X-COM: UFO Defense/Enemy Unknown
There can be no other. If you've not played this game before, see if you can get your hands on a copy of the July 2000 issue of PC Gamer, with the CD. Beg, borrow, or steal as necessary because it's damn hard to name a game with more replay or entertainment value than X-COM. (The game had the subtitle UFO Defense in the US and Enemy Unknown in the UK.)
• Space Sim: FreeSpace 2
FreeSpace is probably the best mission-based space sim I've played ever. I typically prefer more open-ended space-sims, but look at the options... FreeLancer fell flat, having been released with an
entirely static universe and a braindead AI. The next most recent option would be the Privateer series, which is now too old to be compatible with most input devices (assuming you can trick it into running on a Windows box).
• Traditional Sim: Silent Hunter II
First, I've not picked up Silent Hunter III, yet, so it could very well be a better game. Silent Hunter II just knocks my socks off in terms of realism and tension. If you think it takes zombies to make a game scary, wait until you're commanding a German U-Boat, listening to those allied destroyers closing in on the surface. When you start hearing splashes and realize you've lost this round of cat-and-mouse, you'll be about ready to jump out of your pants.
• RPG: Planescape Torment
There can be no other. To start off with, Planescape is my favorite D&D setting. The developers did a wonderful job staying true to the setting too. Moreover, the character you play is built in such a way that you can play him however you want to, and it fits. Dialogue options and NPCs are built to give you wide-open gameplay, without making it too easy to stray from the campaign's plot line. Unfortunately, Torment's only downside was that it failed to set a trend. To this day, RPGs are either plotless micromanagement RTS's, like the Diablo series or any MMORPG you can name, or they never leave the relative safety of the [Better Left] Forgotten Realms.
• Racing: n/a
Actually, I'm still looking for a good (and relatively recent) racing game for the PC. With the Need For Speed series taking the route of the ricer-racer, I'm left wanting when looking for a game using high-end sports cars or going off-road for something akin to World Rally Racing.
• Freeware:
MegaMekIt's already been mentioned, but it deserves to be mentioned again. If you think MechWarrior and MechCommander have strayed too far from their BattleTech roots, download MegaMek. If you want to see a tabletop game faithfully transfered to the computer screen, download MegaMek. If you're just looking for a badass strategy game, and only have about $1.20 in your wallet, save the cash for food, and download MegaMek.