I've collected the hacks, house rules and new material for OSH that I've found on the forums. There's some good stuff that I don't want to be lost in between threads that are no longer useful.

I hope this is useful. Please let me know if it can be improved.

---HOUSE RULES---
new: LETHALITY, APOCALYPSE WORLD AND GEARS OF WAR
http://forums.oldschoolhack.net/discussion/67/rules-hacks-lethality-apocalypseworld-gearsofwar

new: FREE TALENT AT FIRST LEVEL
http://forums.oldschoolhack.net/discussion/77/starting-at-second-level

POWERING MONSTER ABILITIES THROUGH AWESOME POINTS ALONE
Instead of giving monsters abilities, buy them as you need them by chucking AP into the Bowl.
http://forums.oldschoolhack.net/discussion/11/awesome-points-and-the-osh-monster-collection

WEAPON DISADVANTAGES
Weapons lose their advantage in a certain arena type.
http://forums.oldschoolhack.net/discussion/24/weapon-disadvantages

REORDERING THE TURN SEQUENCE
Impede more than just movement.
http://forums.oldschoolhack.net/discussion/29/reordering-the-turn-sequence/#Item_2

DING! GAINING A LEVEL MID-COMBAT
http://forums.oldschoolhack.net/discussion/40/ding-gaining-a-level-mid-combat/#Item_1

CREATING MONSTERS
A new way of creating monsters.
http://forums.oldschoolhack.net/discussion/41/monster-stat-blocks/#Item_2

NEW SCHOOL OLD SCHOOL HACK
A different XP system and separate races and classes.
http://forums.oldschoolhack.net/discussion/48/new-school-old-school-hack/#Item_9

DICE POOLS AND WAGERS
http://forums.oldschoolhack.net/discussion/60/dice-pools-and-wagers/#Item_1

---IDEAS FOR NEW MATERIAL---
DESPERATION ATTACK
A power usable when you've been badly injured.
http://forums.oldschoolhack.net/discussion/9/additional-rule-concept-desperation-talent

MAGIC ITEM IDEAS
http://forums.oldschoolhack.net/discussion/12/lets-talk-loot-rules/p2

REVERSE OLD SCHOOL HACK
Playing the bad guys.
http://forums.oldschoolhack.net/discussion/25/reverse-old-school-hack

NEW ACTION IDEAS
http://forums.oldschoolhack.net/discussion/57/impede/#Item_4

GONZO MAGITECH LAND
A dozen or so new classes.
http://forums.oldschoolhack.net/discussion/26/setting-hack-gonzo-magitech-land/p1

NEW CLASSES
The Druid and Monk.
http://forums.oldschoolhack.net/discussion/35/problem-with-niche-protection

MONSTER POWERS
http://forums.oldschoolhack.net/discussion/22/monster-poowweerrs

HIRELINGS
http://forums.oldschoolhack.net/discussion/45/some-thoughts-on-hirelings/#Item_5

REDBOX HACK
Converting your favourite classes.
http://forums.oldschoolhack.net/discussion/52/converting-redbox-hack/#Item_10

CAMPAIGN IDEAS
The Realm of the Dead, Arabian Nights, Old Steam Hack, Pirates and a Magical University
http://forums.oldschoolhack.net/discussion/33/realm-of-the-dead
http://forums.oldschoolhack.net/discussion/14/arabian-style-setting
http://forums.oldschoolhack.net/discussion/59/old-steam-hack-a-playtest/#Item_4
http://forums.oldschoolhack.net/discussion/37/need-advice-on-some-set-pieces
new: http://forums.oldschoolhack.net/discussion/65/two-settings-for-osh/#Item_1
new: http://forums.oldschoolhack.net/discussion/76/arr-old-school-pirate-hack

POWERS
http://forums.oldschoolhack.net/discussion/61/adding-powers-to-osh/#Item_1

OLD SCHOOL WARFARE
http://forums.oldschoolhack.net/discussion/50/old-school-warfare/#Item_4

COOL EFFECTS
On fire, hamstrung, etc.
http://forums.oldschoolhack.net/discussion/38/any-other-wednesday/#Item_6

ADVENTURE IDEAS
Don't visit if you're going to AntiCon
http://forums.oldschoolhack.net/discussion/58/feedback-on-first-session-idea-anticonners-stay-out/#Item_1

---ADVICE & RESOURCES---
SYSTEM REFERENCE DOCUMENT
http://forums.oldschoolhack.net/discussion/69/old-school-hack-srd

GMING ADVICE ON CAMPAIGNS AND ADVENTURES
From the author himself.
http://forums.oldschoolhack.net/discussion/15/throwing-together-an-adventure-and-running-a-combat

THE O.S.H. ICONS
http://forums.oldschoolhack.net/discussion/comment/94/#Comment_94

WHAT DOES HEROIC/A CAMPAIGN LOOK LIKE?
http://forums.oldschoolhack.net/discussion/36/what-does-the-heroic-game-look-like/#Item_8
http://forums.oldschoolhack.net/discussion/21/a-full-on-old-school-hack-campaign/p1