When I had regular game nights with a group of friends, I modified Scrabble by making up a deck of cards with rule exceptions on them, like allowing a proper name, bonus points for a word from the Simpsons or LOTR and so on. We would distribute them randomly before we started to play. They were pretty fun.
There’s too many cards and rules already, and you want to ADD rules to it? I’ve played with people who have all the (then-)current cards, and games easily took 3 or 4 hours.
This wasn’t deliberate, but I once played a Scrabble game where we didn’t know you coudn’t go diagonally. I went down all the double and triple word scores on the lower right, and got over 1,000 points with one word.
This one?
My family played a variation of BattleShip.
ON your turn you got one shot for each ship you still had afloat. The kicker was that you announced all of your shots at once and then your opponent told you if you had hit anything. And he wouldn’t tell you which one was the hit. Just that one (or if you were lucky, two) of your shots were hits. The strategy was trying to figure out which of your shots hit his cruiser etc. This made for a faster game.
I recall a movement some years ago to try and introduce “House Rules” to Tournament Play for Mornington Crescent, notably the “Royal Flush” rule which would allow the player to jump immediately from Victoria Station to Waterloo, even if they were in Knidd, waiting for an adjudication, or (most controversially), caught in the Dollis Hill Loop.
Fortunately, the “House Rules” movement never really caught on outside the Soviet Union at Inter-Russia Tournament level, where they played with the “Stalin Decree”- any player who attempted to go back to a previously played station would be shot in the back by the NKVD.
Fosbury’s A Brief History Of Mornington Crescent (and subsequent reprints) contains a very readable section on some of the more notable house rules, and the subject is covered at length in Bryson’s highly recommended Mind The Gap: The Complete Guide to Mornington Crescent, although it has been out of print for some years now, pending the completion of the Jubilee Line extensions.
On a more serious note, we used to play Monopoly with “Monopoly Cheques”.
Landed on Mayfair with Hotels and didn’t have the cash to pay for a room at the Ritz up front? Not a problem; just write a Monopoly Cheque. The Bank would front you the money, and you had three turns to come up with the cash to reimburse them, otherwise they’d seize your properties to the value of the “bounced” cheque.
We also had an “Airstrike” rule in Battleships, which could only be used once per game, and only if the player still had the Aircraft Carrier, which would simultaneously strike all squares in a 3x3 square radius.
Indeed. The only house rule I have for Killer Bunnies is: No Killer Bunnies in my house. 
1 torturous 3-hour game ending in a random determination of the winner was enough for me.
We’re trying to come up with house rules to make the Doom boardgame even remotely fair and balanced. We’re going to try unlimited pistol ammo the next time we play. (Which nobody wants to do until I finish painting the figures, grump grump.)
After further review, I recall that we did have a minor house rule for Killer Bunnies: Whenever referring to the weapon “Sharks WFLBs,” and there was a good reason to use the full title, you had to speak in the style of Dr. Evil.
I have this argument every time I play Battleship. Every time, the person I’m playing against either insists that you get one shot per turn, rather than one shot per ship (so 5 shots at the beginning), or that you AREN’T supposed to tell them that you sunk something (one guy would say that you’re only supposed to say if your Battleship was sunk, because the kids in the commercial used to say it)
Not a rule variant, but these: http://www.otb-games.com/apples/apples_blank.html greatly increase the fun factor 
I’ve never had a problem with it. But that may be because of our own house rules.
Craft can be increased by winning spirit or psychich combat
Characters are more fun when you play their alignment EG Good characters don’t attack each other.
A friend of mine made new rules for the card game “war” to add a bit of strategy to it.
I don’t remember exactly how it went, but it added some actual decision making. Now that I think about it, it was probably more of a complete rules revamp than a house rule.
Also, I played Monopoly by passing out the properties randomly at the beginning of the game, and giving everyone 5 minutes to make trades and buy houses before the game started. It’s over in like 30 minutes that way.
Apples to Apples – Love that game. Our reasoning is always pretty arbitary. I am known to reject communism and anything related to it, because “Communism is dumb”.
In my recent trip to Sacramento, we played using what my friend (an insider in the gaming community… ) referred to as “The Baron Munchausen” variant. As the judge, as you put down cards, you had to tell an amusing tale. Using the cards. ie: “Once, while Marie Curie was travelling to Mexico via the recently refloated Titanic, they were sunk by * the USS Missouri*, which just goes to show you shouldn’t tempt fate.”
Hilarity usually insues.
Risk– We had several house rules for Risk.
1- No territory can have more than 50 troops.
2- When turning in cards, after a certain point (65?) the industrial capacity of the world is destroyed via war, and the count starts over again… at 3.
3- No territory hopping. Standard example: From Central America, you could take, say, Venzuela, then use that army to either go one more (into Brazil, maybe) or you could split it up and hit Brazil and Peru, but that was it. No going from Central America to Venezuela, to Brazil, to North Africa, to Western Europe, to England, to Iceland…
Our rules made the game take MUCH longer, but also added a lot more strategy to the game.
There’s a book called Beyond Boardwalk which has a very clever re-engineering of the rules of Monopoly to make them quite a bit more fun and balanced and skill-intensive. The main one is to double the cost of all properties, and then play with the (rarely used but present in the actual rules) auction rules. In normal monopoly, during your first n turns it’s correct to buy whatever you land on 98% of the time (with the possible exception of the utilities). If they cost twice as much, that is much less clearly the case, and then there’s an auciton, where players’ ability to evaulate the game state becomes relevant.
More “out there”, in college, we would take two monopoly boards, one in English and one in Russian (because we happened to have Russian monopoly, not because anything about it was special), and put one board’s Free Parking on top of the other board’s Go, making a huge figure 8 with 2 of each monopoly. If you owned the same monopoly on both boards, the rent was doubled. And the railroads continued to go up in value if you owned 5, 6, 7 or 8 of them. Good times…
For Carcassonne, we play that the starting player flips up n+1 tiles, where n is the number of players. Each player then plays one of the revealed tiles. Then the next player (the person to the previous starting player’s left) flips up n+1, and so forth. This adds a LOT of strategy and decision making without being overwhelming.
We changed the rules of Pictionary so much that it was a completely different game, with no board and no cards. I’ve posted a description here.
My favorite way to play Taboo is where you don’t actually get to see the list of taboo words, so you just have to kind of describe the thing you’re trying to describe in an ass-backwards way and hope for the best.
What house rules did you use to avoid the “whoever sits after the prophetess is consistently and royally screwed” thing?
Honestly, it’s never been a problem. If it were discarding the adventure card she didn’t choose would solve things.
Good thing James Cameron never heard of your house rules. That movie was long enough without cold-water sharks and piratical lifeboat crews!
Can’t tell for sure. The box picture is different from the one we had (actually still have, but a lot of the pieces are missing). When the Titanic movie came out we searched high and low for the parts in hopes that we could get a good buck for it on ebay, but to no avail. The parts we did find were in such crummy shape no one would have paid a dime for it.
When my family played Scrabble, we always played with a regular dictionary and allowed only standard English words, instead of the official Scrabble dictionary which allows goofball words like “shat” and “aa”. This made it more of a game of strategy and less of a game of memorizing weird letter combinations that no normal person would ever use.