These are the current task and their rewards. You talk to a postman NPC to start a task. This will be reworked completely in due time.

Gold Rewards
Task    Reward
100 Rats    500 gp
100 Cave Rats    750 gp
100 Snakes    750 gp
100 Bugs    900 gp
100 Wasps    1,200 gp
200 Lions    3,000 gp
200 Scorpions    4,500 gp
Item Rewards
Task    Reward    Class Restriction
50 Trolls    1 Iron Helmet    None
100 Dwarves    1 Plate Armor    None
200 Minotaurs    1 Plate Legs    None
200 Skeletons    1 Dark Helmet    None
500 Swamp Trolls    1 Serpent Sword    None
1000 Elf Arcanists    1 Wood Cape    Paladin Only
300 Wild Warriors    1 War Hammer    None
200 Dragons    1 Dragon Lance    Knight Only
1000 Demons    1 Demon Legs    None
5 Grorlams    1 Giant Sword + 6,000 Exp + 3,000 gp    Knight Only

Experience Rewards
Task    Reward
200 Necromancers    58,000 Exp
200 Orc Leaders    27,000 Exp
200 Orc Warlords    67,000 Exp
200 Orcs    7,000 Exp
50 Dworc Voodoomasters    5,000 Exp
200 Elephants    16,000 Exp
100 Black Knights    320,000 Exp
100 Demon Skeletons    12,000 Exp
200 Elves    8,400 Exp
300 Elf Scouts    22,500 Exp
200 Spiders    3,600 Exp
200 Behemoths    250,000 Exp
200 Banshees    90,000 Exp
200 Ancient Scarabs    72,000 Exp
200 Amazons    6,000 Exp
200 Crocodiles    12,000 Exp
300 Dark Monks    21,750 Exp
300 Dwarf Guards    24,750 Exp
100 Dwarf Geomancers    24,500 Exp
200 Dragon Lords    210,000 Exp
200 Dwarves    4,500 Exp
200 Elder Beholders    56,000 Exp
200 Fire Devils    22,000 Exp
200 Ghosts    24,000 Exp
200 Heroes    120,000 Exp
100 Green Djinns    19,000 Exp
100 Blue Djinns    19,000 Exp
100 Liches    90,000 Exp
250 Hydras    262,500 Exp
200 Hunters    22,500 Exp
100 Serpent Spawns    100,000 Exp
100 Scarabs    9,000 Exp
100 Terror Birds    11,250 Exp (repeatable 3 times)
300 Warlocks    600,000 Exp