Menaphos Scarabs (~300k xp/h using an alt to hop worlds. No combat XP gained)
Daily activities:
Master jack of trades aura x2 (reset with vis wax)
Daily slayer challenge (extended with vis wax, completed via co-op slayer)
Dwarven instinct aura (chances at small XP lamps)
Player owned ports (Build 4 parrot totems and 3 human skulls. "Block" as many of the irrelevant adventurers as possible on 3 of the ships by never clicking on the returned voyage)
Lucky ports challenges (medium xp lamp reward). You can get one from Yanille crystal tree every 48h
Event Cards from J-Mod events
Weekly activities:
Broken Home replay (after completing the challenges, it gives a huge XP lamp each week the quest is replayed, use this guide for 20-25 min speed runs)
Penguin hide and seek (complete Cold War and Hunt for Red Raktuber for extra points. Try to save weekly reset tokens for weeks when all 10 pengs can be spied)
Capping at the citadel (fealty bonus from the clan cloak)
Meg at Player owned Ports (1/9 chance of getting a slayer lamp)
Monthly activities:
Troll invasion (fighting). Use monthly reset token on this activity. Recoil the trolls (blood amulet helps too). Use aggro pot or tag the diseased trolls to make the aggressive. If you're tagging,reduce attack to 0 with sara brew before attacking. The boss troll can be pushed towards the wall for faster kill by walking one tile at a time towards him.
God statues (Use sara brew to tag, then recoil. Blood amulet speeds up the kills significantly)
Misc:
Soul Wars (Not recommended as it's very slow). Activity bar is kept up by healing teammates, burying bones (does not give prayer xp) or fighting players (make sure PvP XP is off). Potential fc: "soulwars1"
Anima Islands (Not really worth doing either unless you're an ironman skiller). It's 100 mins per large lamp if you get 100% in the games, which makes it slightly faster than Soul Wars for Slayer. You get no Thaler in this minigame though.
Looting airuts (collecting tuska mask pieces). 20 masks = 400 slayer points = 10k slayer XP. Not a fast XP gaining method, but the GP/H can be quite nice and you can disassemble for invention while looting.
The Arc (roughly 1 huge lamp every 5 hours)
Vic the Trader every 6 months
Quests and other non-recurring activities:
Stronghold of Player Safety (2x500 xp lamps)
Varrock Museum (1000 xp after completing Natural History quiz and 3x1000 xp lamps if slayer is level 20+ while earning kudos)
Swept Away (10x (10*slayer_level) xp lamps)
Combat Academy (Reward book equivalent to a small xp lamp)
Broken Home (as mentioned in the weekly activities, gives huge xp lamp when the first challenge is completed, also replayable each week for a huge lamp when all 3 challenges have been completed)