Three words. World of Goo.

Just got it, and it's awesomely amazing.

I got my wife hooked on Guild Wars.   Later we moved to L4D and soon L4D2.

I also built her a Warhammer 40k army (she has a heavily house-ruled sisters army) and we've played Space Hulk together.

To top it off, she's a player in my monthly D&D game.

It's a nice feeling.

My wife likes Tropico...give that one a try.

My wife is a gamer too but she's mostly into those stupid FaceBook apps. Something called Farmville, YoVille, and something else that looks stupid. She's also into the Sims 3. I got her into WoW when I played it. She likes Prototype which I find funny because that's normally not her style of game. Surprisingly she likes Batman Arkham Asylum and she always gets me to buy her the latest Guitar Hero. I just got her part 5 the other night when I grabbed myself Win 7. She likes some console games too, mostly Mario Galaxy, things like that.

Still just as the OP said, I wouldn't call my wife "a Gamer" like most of us here.

Try games that have some combination of:

A) Don't take huge amounts of time.

Involve socializing/customization.

C) Aren't based solely on violence: sometimes this is a bit of a crutch for the industry - people know how to make combat so they use it to extend a game's length.

D) Have some atmosphere/style/wit that makes them interesting.

Within my generation, I'm sure the proportion of women that would call themselves gamers is quite small compared to the proportion that have fond memories of cleverly written Lucusarts adventures like Day of the Tentacle, for just one example amongst many.

Looking at the earlier posts, I think World of Goo and Tropico are really great examples. They just ooze fun and silly gorgeousness, you don't have to have a special interest in gaming to see the appeal.

I must be the only person left not on facebook, guess i'm the loser now haha.

I picked up an extra copy of Guild Wars: Prophecies at the local closeout store.  I'll spring that on her in another couple of weeks, once NWN is further in the past. 

It's not that she's not exposed to games - quite the contrary!  But if I were forced to get her a videogame for her birthday, I have no idea whether she'd actually play it.

World of Goo is truly fantastic!  But she's not interested.  Ditto for the Facebook games (except for the truly fantasic part).  She's amused by the recent Monkey Island releases, but not enough to play them.  (Although she's in tune with their wit - she's quickly figured out some of the sillier puzzles)

She does like Gish multiplayer.  She can't help but "grrrrrrrr" when she makes her character "heavy" 

I'll have to investigate Tropico !

Some thoughts on why your wife likes what she likes:

1.  Easy introduction, but deep gameplay.  Neverwinter Nights has a lot under the hood, but the gameplay itself is pretty easy point and click.  All of popcap's games fall under this umbrella, which is why Plants vs. Zombies is no suprise.  Even Demigod has been labeled as a beginner RTS, in that you only have the one character to worry about.

2.  More of the carrot.  Rewards!  Rewards create addictive gameplay.  Plants vs. Zombies is loaded with them, as is Neverwinter Nights.  As is Demigod.

3.  Obvious sticks!  Most good games have something good that you're toying around with, and something else you're trying to avoid.  All of the games you mention have very obvious sticks - avoid death!  Don't let the zombies by! 

4.  Quick restarts.  In Plants Vs. Zombies, if a zombie gets by, you can restart the level very easily.  In NWN, quick saves work wonders, and even if you don't have a good save point, you restart at the temple.  Demigod makes you sit out for a minute, but then you can game again.

5.  Lets face it - they're easier to win at.  Once you learn the basics, you can breeze through Plants vs. Zombies with only a couple losses.  Depending on the difficulty level, Neverwinter Nights can be the same way.  These are either single player, or co-op games, so this goes easily.

The more interesting thing is trying to figure out what she doesn't like in games, and so you know what to avoid.  While its hard to gather from just a list of games that "hit" with her, here's my thoughts:

1.  How do you play this @#&$*^ game?  A lot of the "gamer" games have complex control schemes that require a good bit of getting used to.  Sure, FPSes come natural to gamers, but teaching them to run around and shoot something on a map is hard enough.  Add in skills and special abilities, and this can get crazy.

2.  Help!  I'm lost!  A lot of FPSes and RPGs require a lot of attention as to where to go.  If you're worried about how to walk and shoot, you'll miss the sign that hints at where you are supposed to go.  Neverwinter Nights is really direct about what you need to do and where you need to go, and I'd imagine its even easier with a guide there to help.

3.  I died again, I don't get it, I can't play this stupid game.  I'd tred lightly with Tropico for this reason - there is so much to juggle, it gets very overwhelming.  You can lose because of a military coup, the Americans or Soviets kicking you out, you lose an election, or rebels fight and take over.  What can make these games worse is that you have to start over when this happens - you lost, try again.  Sure, Plants Vs. Zombies does this, but you haven't spent an hour getting to that point just to start over.

4.  I'm just no good at this game.  Competitive multiplayer games mean that beginners lose well more than half the time, which is not forgiving.  It makes it hard to get into and stay enthusiastic about.

Some suggestions for you:

Single Player:

Puzzle Quest.  Bejeweled with theme!  Easy to pick up and get into, lots of carrots.

Crayon Physics.  A lot of fun to play through the levels.

Torchlight - Comes out today online.  Should be easy for her to pick up, and will give you a good idea if she'd like to play Diablo 3 with you.  If she really digs it, you can grab Titan's Quest for you both.

Peggle.  Addictive!  Try it out online for free.

Mevo and the Grooveriders - a cute rhythm game.

Rollercoaster Tycoon 3.  A great introduction to an economic sim game, hidden under the shiny guise of a theme park.

The Sims/2/3.  A  great juggling act, following the successful line of thought that if you have a million things you want/need to do, but only so many things you can do, it stays challenging.  Lots of carrots with shopping.

Multiplayer:

Audiosurf.  Pick her favorite music, run along and pick up colored blocks to score points.  Theres no "losing," just low scores and high scores.

Warhammer: Dawn of War 2.  What!?  That game's insane!  Yeah, but the campaign is co-op, and you get new items and level up your squads between missions.  Theres also a new last stand mode, where you can play with her and one random chap against wave after wave of oncoming monsters, trying to better your score.

Congratulations, you're married to what we in the biz call a "casual gamer" game suggestions, I second Peggle (multiplayer is specially addicting with a willing partner/victim), and I'll add both Braid and Droplitz to the mix.

And I know this is gonna sound very weird but... err... how about Left 4 Dead? women in general tend to look at the whole 'zombie' thing not too kindly and it *is* a violent game (in that juvenile, 10-liters-of-high-pressure-blood-per-meatbag way so prevalent in horror movies), but perhaps the way the game forces cooperation with other players may entice her to play it.

Take the opportunity to win while you can. It's the only time you'll get to beat your wife at anything

If ANY game will hook someone, Neverwinter Nights definitely fits the bill.  Obviously, you could dip into NWN2 with her as well.  If she can handle the Sci-Fi genre, Mass Effect will definitely satisfy her.

Outside of that, you could try some of the Diablo clones, such as Sacred 2 or Titan Quest (both real good games).  You can get both off of Direct2Drive dirt cheap.

My fiancee was hooked on World of Warcraft for years, and only stopped playing because work and social stuff started to take all of her gaming time away.  We used to play the game together regularly.  Now we're waiting for that "next game" to play together.  Unfortunately her PC is pretty much toast but we can't afford to replace or upgrade it. 

My wife used to play Doom and Quake with me a lot back in the day.  But nowadays she will play the Nancy Drew and CSI type "puzzle" games.  She also likes Tropico.  Most of the time though she places those Facebook games that suck your lifeforce. 

All I know if my wife cares not if I play a game for hours on end.  She'll do her thing (watch TV, knit, game) and I'll do mine.  I guess that's what happens after being married for 13 years, you just want your own space, none of this "but we need to watch TV with each other every night".  It's more like "can you play your game tonight so I can watch this movie you hate and knit."  No problem dear! 

lucky bastards