House rules in Monopoly
Here's a few I know of, please tell me of any other ones:
all money paid in fines goes into a pile that is claimed by anyone landing on Free Parking
No one does any trading until all properties have been bought (I'd hate that one, it could make the game drag on for hours)
Selling a hotel gets you half the price of a house and four houses. (Many people are surprised to realise this one isn't in the rules, but the rules are very clear when you read them - when you sell a hotel, you get half the price you paid for it and half the money you paid for the four houses. This rule is devastating tactically becasue of the 'build evenly' rule - you sell just one hotel and everything you've built has to come down. Our family only build hotels when we're very very certain we can afford the risk)
Variations on 'get out of jail free'. Does the card allow you to leave jail after rolling the dice? I think the rules probably don't intend it this way, but there is a bit of ambuiguity.
A lot of people forget the 10% interest when demortaging and transfering mortgaged property between players.
The rules as written tend to reduce the chance element in the game (though it is always there to a fair extent) I usually play to the rules, simply because it eliminates potential friction between players used to different house rules. It gives an ultimate arbiter when players suddenly realise they have different assumptions.
I enjoy my games without arguments, so finding ways to eliminate them in advance is useful. Competition is fun, arguments/vinditiveness are not.

no subject
"Pay rent when mortgaged": Rental on properties can still be collected when the property is mortgaged.
That rather misses the point of mortgages!
"Pass instead of auction": Properties are not auctioned by the bank if a player passes on it. (My sister and I always played this rule as it is better in a two-player game.)
Sounds like you're missing a better option which is within the rules. Remember that there is nothing in the rules to forbid the player who refused to buy at the list price from bidding in the auction. I find the use of this tends to bring prices down to sensible levels in two player games.
"Income Tax on Cash": Income tax is calculated on cash rather that total worth, because that is a pain to calculate.
er. Income tax is flat rate, not a percentage.
"Demolish evenly rule": Houses must be demolished as well as built evenly.
That is how the rules read anyway.
For tactics, btw, some people are unaware of the "building shortage" rule which fixes the number of houses at those the set came with. Block other players with four houses on Baltic Avenue.
Every time - grin. Though astute players will note the rule on auctioning houses when the stock falls low and that benefits the players with more expensive houses.