Wow! Nice! I've only played the basc game, so no house rules.

We have a couple we like:
1) Who goes first? Everyone rolls the dice. The person with the highest roll gets to choose where in the order they want to be (often people pick going 'last' .. aka 'middle' so that they can place both their initial settlements at the same time)
2) Robber: Sometimes we re-roll the first two 7s each person gets to make the game go a bit faster.
....
I will post any others I think of.

Jeanne

Here are a few:

1) At the start of the game, take resources adjacent to both initial settlements. This helps quicken the pace of the game at the start. Because of the possibility of player 3 or 4 losing half their resources prior to any chance of building, should a 7 be rolled early, a special building phase is in effect for the first circle of turns.

2) Extortion. The robber and victim can negotiate over which resource the robber will take from the victim's hand, in exchange for the victim being allowed to choose upon which hex the robber is placed. [see prior thread]

3) Futures. Allow trading for a future resource that a player might earn. Futures must be settled at first opportunity.

4) Charity. Have too many cards in your hand? Afraid that a 7 is going to be rolled? Build automatic karma points by giving away your excess resources before the roll.

The group I used to play with often increased the number of victory points to win the game. This necessitated the use of development cards to win.

Also, we would give points for knight combat... if you displace an opponent knight with one of yours, you get a point. This made the strategy risky though, because then you might not have enough strength of knights to defend your cities from the barbarians when the land (we didn't play with this option with the communal defense variant, only the individual defense variant).