Without further adieu:
Other People's House RulesEvery one of these is something someone else came up with originally.
Synopsis: This house rule comes from Semper Initiativus Unum. The basic idea is that magic users and spell casters can cast some spells outside of combat without preparation if they pay gold and take a large amount of time.
Purpose: This gives magic users and clerics a deal more flexibility. The idea is to get their utility spells into circulation, since (especially at lower levels) caster slots are limited, and they tend to go for things that are likely to be useful in combat. Specifically, the rule is structured to make it progressively less desirable to not prepare higher-level utility spells if you want to use them.
Experience: Obviously this hasn't seen a lot of use in my campaign, but it has seen some. We've been very short on magic-users in general, but our elf has done this once with detect magic. Both I and his player appreciated the ability to do so, even if it didn't net him anything in the instance.
Verdict: Cautiously optimistic
XP for gold spent
Synopsis: This is an old one. The basic idea is that PCs earn experience not for simply bringing treasure back to civilization, but for spending it in actions that don't directly benefit them as adventurers. The Mule Abides has a pretty good writeup that ties it to The First Fantasy Campaign.
Purpose: This primarily accomplishes two things. One is splitting the PCs' resources and forcing them to make decisions about what to spend coin on, since buying e.g. armor doesn't count for xp.The other is provide some verisimilitude for xp gain.
Experience: I don't give a fig for the verisimilitude argument, but I do like forcing decisions on the players about what to do with their loot. Not only does it allow me to give them more loot, but it also allows me to restrict how much coin can be spent on adventuring supplies without the players having no recourse but to stockpile coin. Poor adventurers are good adventurers, after all. Further, there's another side effect: it increases player 'buy-in' for the world as they interact with it in ways different from just treating it like a backdrop for the dungeon. Our best session to date was mostly spent roleplaying with NPCs and finding ways to dump coin on them.
Verdict: I highly recommend this house rule precisely because it broadens the players' conception and care about the world. I'm having a lot of fun and the players are having a lot of fun.
Synopsis: This one's simple: if a person is down between 0 and 2 hp inclusive, you can spend a turn to bandage them up. This returns 1 HP, and can only be done once until they heal. Further, characters regain 1 HP per full day of rest.
Purpose: This provides some very limited low-level healing, and it reinforces the idea to the players that they're hurt and should consider turning back - or pushing on, but in the knowledge that they're taking a huge risk. You'd think that the numbers on the sheet would do that for you, but it's nice to have another indicator. Plus it's another chance for a trade-off: do the players want to patch up their buddies, restoring 1 HP but risking the chance of a wandering monster?
Experience: The players like it, and it doesn't seem to significantly cut into the mortality of the game; a lot of PCs and NPCs have still died. It's easy to keep track of, too - you can just do it in your head. Plus, it gives me flavor in describing hurt people and how they feel. I'm in favor.
Not dead at 0 HP
Synopsis: My implementation of this common rule is as follows: at 0 HP you're unconscious, at below 0 you're dead. However, if you go below 0 HP, and someone can bring you back to 0 or above before the round is over, you might live.
Purpose: It puts a small wedge of 'not okay' betweeen D&D's much-discussed 'you're fine' and 'you're dead' without making that wedge large enough to significantly affect vitality. It also gives the players some hope when a beloved NPC or PC goes down.
Experience: Bringing someone back up from negative numbers is a very difficult task, since most spells take the full round to come into effect, which means you basically have to anticipate when someone is going to need healing. However, the 0 HP bit has come up a decent bit more often, and it has been fun for all concerned because of the relief from surviving such a near brush - which the players actually feel is very near, since if the dice had rolled 1 higher, their characters would be dead. It has also added fun in some instances where the PCs weren't sure if someone was dead or merely unconscious and bleeding out. I'm in favor.
XP for gold hoarded
Synopsis: For whatever reason you care to justify, the PCs have to sacrifice their gold for XP without doing anything else with it. This is different from XP for gold spent above because it's not just spending gold on things that 'don't matter' - it's not spending the gold at all until they get enough to level up and make a trip to one of these sacrificial spots
Purpose: This was meant to provide an in-game excuse for the existence of class levels, because I think justifying such things inside the game is cool. It was also meant to put the squeeze on treasure, forcing the PCs to make a decision as to whether to spend their hard-earned gold on adventuring advantages or XP.
Experience: In reality, it meant that the gold either sat there being useless like a millstone around the players' necks, or much more likely they dipped into it too far and too fast, meaning they never accumulated appreciable XP-substitute. Either way, they got no experience whatsoever, so it felt to me and to them that they were stagnant. I really don't recommend this.
Alternative: I still have places I call 'navels of the world' in my game where a person goes to suffer strange and weird rituals and be granted class levels, but now I grant XP for gold spent, as above, and the rituals themselves are a mere tax - the square of your current level * 100 gp to advance.
All in all I'm happy with the house rules I'm using. There are plenty more I have that, so far as I know, aren't someone else's invention. There are probably others that are, but are so central to the usual play for the game that I just don't see or remember them as house rules.