Here are Prayers, the Gods who grant them and what level is required to use them.
Truth God
Lvl 1: Holy Knife, 5 % Attack boost
Lvl 11: Holy Rapier, 10 % attack boost
Lvl 21: Holy Spear, 15 % attack boost
Lvl 31: Holy Sword, 20 % attack boost
Lvl 41: Holy Longsword, 25 % attack boost
Lvl 51: Holy Club, 30 % attack boost
Lvl 61: Holy Mace, 35 % attack boost
Lvl 71: Holy Handaxe, 40 % attack boost
Lvl 81: Holy Battleaxe, 45 % attack boost
Lvl 91: Holy Warhammer,50 % attack boost
Loki, God of Lies
Lvl 2: Unholy Knife,5 % Strength boost
Lvl 12: Unholy Rapier,10%Strength boost
Lvl 22: Unholy Spear, 15%Strength boost
Lvl 32: Unholy Sword, 20 % Strength boost
Lvl 42: Unholy Longsword, 25 % Strength boost
Lvl 52: Unholy Club, 30 % Strength boost
Lvl 62: Unholy Mace, 35 % Strength boost
Lvl 72: Unholy Handaxe, 40 % Strength boost
Lvl 82:Unholy Battleaxe, 45 % Strength boost
Lvl 92: Unholy Warhammer, 50 % Strength boost
Hepheastos, The Metal God
Lvl 3: Hardskin, 5 % Defence boost
Lvl 13: Rockskin, 10 % Defence boost
Lvl 23: Copperskin, 15 % Defence boost
Lvl 33: Bronzeskin, 20 % Defence boost
Lvl 43: Ironskin, 25 % Defence boost
Lvl 53: Steelskin, 30 % Defence boost
Lvl 63: Saphriteskin, 35 % Defence boost
Lvl 73: Emeriteskin, 40 % Defence boost
Lvl 83: Rubiteskin, 45 % Defence boost
Lvl 93: Dimoniteskin, 50 % Defence boost
Arandi, The Elf Mother
Lvl 4: Goodeye, 5 % Archery boost
Lvl 14: Keeneye, 10 % Archery boost
Lvl 24: Sharpeye, 15 % Archery boost
Lvl 34: Farsight, 20 % Archery boost
Lvl 44: Hawksight, 25 % Archery boost
Lvl 54: Hawkeye, 30 % Archery boost
Lvl 64: Eaglesight, 35 % Archery boost
Lvl 74: Eagle eye, 40 % Archery boost
Lvl 84: Elvensight, 45 % Archery boost
Lvl 94: Elveneye, 50 % Archery boost
Leonardus, God of Magyk
Lvl 5: Mystic Way, 5 % Magyk boost
Lvl 15: Mystic Word, 10 % Magyk boost
Lvl 25: Mystic Lore, 15 % Magyk boost
Lvl 35: Arcane Way, 20 % Magyk boost
Lvl 45: Arcane Word, 25 % Magyk boost
Lvl 55: Arcane Lore, 30 % Magyk boost
Lvl 65: Ancient Way, 35 % Magyk boost
Lvl 75: Ancient Word, 40 % Magyk boost
Lvl 85: Ancient Lore, 45 % Magyk boost
Lvl 95: Ancient Power, 50 % Magyk boost
Woden, God of the North
Lvl 6: Frostbite, Attacks have a 10 % Chance to freeze opponents for a few seconds
Lvl 16: Frostlore, attacks have a 20 % chance to freeze enemies for a few seconds
Lvl 26: Frostpower, attacks have 30 % chance to freeze enemies for a few seconds
Lvl 36: Frostmight, attacks have 40 % chance to freeze enemies for a few seconds
Lvl 46: Froststrike, attacks have a 50 % chance to freeze enemies for a few seconds
Lvl 56: Frostslam, attacks have 60 % chance to freeze enemies for a few seconds
Lvl 66: Frostlaw, attacks have 70 % chance to freeze enemies for a few seconds
Lvl 76: Frostlord,attacks have 80 % chance to freeze enemies for a few seconds
Lvl 86: Frostking,attacks have 90 % chance to freeze enemies for a few seconds
Lvl 96: Frostgod, attacks have 100% chance to freeze enemies for a few seconds
Fulvia, Goddess of Skills
Lvl 7: Catch of the day, 50 % chance to catch a Treasure chest
Lvl 17: Master Chef, 100 % chance not to burn food
Lvl 27: Lucky Lumberjack, 30 % chance to find a Magpie nest while woodcutting
Lvl 37: Pyromaniac, 30 % chance to get double Firemaking XP
Lvl 47: Geologist, 30 % chance to find a gem while mining
Lvl 57: Blacksmith, 30 % Chance to smelt 2 of the same object
Lvl 67: Master Farmer, all crops grow 20 % faster and are more immune to disease
Lvl 77: Constructor, 100 % chance not to bend nails when building
Lvl 87: Craftmaster, 30 % chance to gain triple XP from crafting
Lvl 97: Skillmaster, boosts Farming, Fishing, Cooking, Blacksmithing, Crafting, Engineering, Mining, Firemaking, Woodcutting, Construction, Hunting and Fletching by 1 level.
The Almighty One
Lvl 10: Posioned Blade, attacks have a 20 % chance to poison
Lvl 20: Entangle, Entangles one enemy who is attacking you for a few seconds
Lvl 30: Athlete, Restores run energy much faster
Lvl 40: Posioned attack, attacks have a 40 % chance to poison
Lvl 50: Resistant, has 40 % chance to not be poisoned
Lvl 60: Mass entangle, Entangles all enemies for a few seconds
Lvl 70: Immunity, has 80 % chance to not be poisoned
Lvl 80: Minor Vengance, upon death all enemies will take damage
Lvl 90: Major vengance, upon half health all enemies will take heavy damage
Lvl 100: Immortal, you will not lose your itemsupon death instead you will mearly respawn where you died with 10 less prayer points as well. This will repeat itself until you run out of prayer points.