It's not perfect and you can add and make your own sort of adjustments. Just a basic one.
I'll add "guides" for each type of Warrior and Mage so the Level range will be every 5 Levels. And the monsters at the very left are what you should be killing in the lower range and the right would be in the higher range. Ok? (The 5 types of Mages are going to be a pain...)
Beginners:
Stay on Maple Island
Mages and Thieves: Green/Blue Snails
Warriors and Archers: Green/Blue/Red Snails, Spores
1st Job
Warriors
Lv10: Green Slime, Orange Mushroom
Lv11: Green Slime, Orange Mushroom, Dark Stump
Lv12: Green Slime, Pig, Orange Mushroom, Dark Stump
Lv13: Same as Lv12
Lv14: Pig, Orange Mushroom, Dark Stump
Lv15: Pig, Orange Mushroom, Dark Stump, Octopus
Lv16: Same as Lv15
Lv17: Orange Mushroom, Ribbon Pig, Octopus, Green Mushroom
Lv18-22: Orange Mushroom, Ribbon Pig, Octopus, Green Mushroom, Axe Stump
Lv23: Ribbon Pig, Octopus, Green Mushroom, Axe Stump, Evil Eye
Lv24: Green Mushroom, Axe Stump, Evil Eye, Horned Mushroom
Lv25: Green Mushroom, Axe Stump, Evil Eye, Horned Mushroom, Wild Boar
Lv26: Green Mushroom, Axe Stump, Evil Eye, Horned Mushroom, Wild Boar, Zombie Mushroom
Lv27: Green Mushroom, Axe Stump, Evil Eye, Horned Mushroom, Wild Boar, Zombie Mushroom, Jr Sentinels
Lv28-30: Horned Mushroom, Wild Boar, Jr Sentinels, Zombie Mushroom
Thief (Claw)
Lv10-14: Green Slime, Orange Mushroom
Lv15: Pig, Orange Mushroom
Lv16-17: Pig, Orange Mushroom, Ribbon Pig
Lv18-20: Pig, Orange Mushroom, Ribbon Pig, Green Mushroom
Lv21-24: Pig, Orange Mushroom, Ribbon Pig, Green Mushroom, Horned Mushroom, PQ
Lv25-26: Green Mushroom, Horned Mushroom, Zombie Mushroom, Alligator
Lv27-30: Green Mushroom, Horned Mushroom, Zombie Mushroom, Alligator, Jr Sentinels
Thief (Knives)
Lv10: Blue Snail, Green Slime
Lv11-14: Green Slime
Lv15-17: Green Slime, Orange Mushroom
Lv18-19: Green Slime, Orange Mushroom, Pig, Ribbon Pig
Lv20: Orange Mushroom, Pig, Ribbon Pig, Jr Sentinels
Lv21-23: Pig, Ribbon Pig, Jr Sentinels
Lv24: Pig, Ribbon Pig, Blue Mushroom, Jr Sentinels
Lv25: Pig, Ribbon Pig, Blue Mushroom, Jr Sentinels, Wild Boar, Zombie Mushroom
Lv26-27: Blue Mushroom, Horned Mushroom, Jr Sentinel, Wild Boar, Zombie Mushroom
Lv28-29: Horned Mushroom, Jr Sentinel, Wild Boar, Zombie Mushroom
Lv30: Horned Mushroom, Jr Sentinel, Wild Boar, Zombie Mushroom
Archer
Lv10-15: Stump, Red Snail, Green Slime, Orange Mushroom, Green Mushroom
Lv16-20: Orange Mushroom, Green Mushroom, Blue Mushroom, Horned Mushroom, Dark Axe Stump
Lv21-24: Octopus, Green Mushroom, Blue Mushroom, Horned Mushroom, Dark Axe Stump
Lv25-30: Green Mushroom, Blue Mushroom, Horned Mushroom, Dark Axe Stump, Zombie Mushroom, Wild Boar
Mage
Lv8-12: Blue Snail, Red Snail, Spore, Stump, Green Slime
Lv13-17: Green Slime, Pig, Ribbon Pig
Lv18-21: Green Slime, Pig, Ribbon Pig, Horned Mushroom, PQ (Lv21)
Lv22-24: Green Slime, Pig, Ribbon Pig, Horned Mushroom, Blubbling, PQ (Lv23)
Lv25-27: Green Mushroom, Bubbling, Horned Mushroom
Lv28: Bubbling, Horned Mushroom, Wild Boar, Zombie Mushroom, Evil Eye, PQ
Lv29-30: Horned Mushroom, Wild Boar, Zombie Mushroom, Evil Eye
2nd Job
Warrior (Fighter)
Lv30: Horned Mushroom
Lv31-32: Horned Mushroom, Zombie Mushroom
Lv33-35: Horned Mushroom, Zombie Mushroom, Evil Eye
Lv36-39: Zombie Mushroom, Evil Eye, Fire Boar, Cursed Eye
Lv40-46: Fire Boar, Alligator, Cursed Eye, Jr Cellion, Jr Grupin, Jr Liona
Lv47-50: Fire Boar, Cured Eye, Copper Drake, Iron Hog
Lv51-56: Copper Drake, Drake, Jr Yeti, Stone Gollem, Wild Cargo
Lv57-60: Copper Drake, Jr Yeti, Drake, Stone Gollem, Dark Stone Gollem, Wild Cargo
Lv61-64: Jr Yeti, Hector, Dark Stone Gollem, Yeti, Tauromacis
Lv65-70: Hector, Stone Gollem, Dark Stone Gollem, Yeti, Tauromacis
Warrior (Page)
Lv30: Horned Mushroom
Lv31-36: Jr Sentinel, Horned Mushroom, Zombie Mushroom, Evil Eye
Lv37-47: Evil Eye, Fire Boar, Leatty, Dark Leatty, Jr Grupin, Jr Cellion, Jr Liona
Lv48-49: Evil Eye, Fire Boar, Leatty, Dark Leatty, Jr Grupin, Jr Cellion, Jr Liona, Copper Drake
Lv50-53: Copper Drake, Drake, Jr Yeti
Lv54-59: Copper Drake, Jr Yeti, Drake, Stone Gollem, Hector
Lv60-65: Cold Eye, Jr Yeti, Hector, Coolie Zombie, Dark Stone Gollem
Lv66-70: Cold Eye, Hector, Coolie Zombie, Dark Stone Gollem, Wild Cargo
Warrior (Spearman)
Lv30-36: Horned Mushroom, Zombie Mushroom, Evil Eye, Fire Boar, Leatty
Lv37-39: Evil Eye, Fire Boar, Leatty, Cursed Eye, Cold Eye
Lv40-45: Fire Boar, Leatty, Cursed Eye, Cold Eye, Lorang
Lv46-50: Fire Boar, Leatty, Cursed Eye, Lorang, Copper Drake
Lv51-55: Copper Drake, Drake, Jr Yeti, Stone Gollem
Lv56-60: Copper Drake, Drake, Jr Yeti, Stone Gollem, Hector, Croco
Lv61-65: Jr Yeti, Croco, Hector, Coolie Zombie, Miner Zombie, Dark Stone Gollem
Lv66-70: Hector, Coolie Zombie, Miner Zombie, Dark Stone Gollem, Yeti
Thief (Assassin)
Lv30-35: Green Mushroom, Horned Mushroom, Zombie Mushroom, Wild Boar
Lv36-40: Horned Mushroom, Zombie Mushroom, Wild Boar, Jr Cellion, Jr Grupin, Jr Liona
Lv41-45: Alligator, Fire Boar, Jr Cellion, Jr Grupin, Jr Liona, Lupin, Zombie Lupin, Copper Drake
Lv46-50: Cursed Eye, Jr Cellion, Jr Grupin, Jr Liona, Lupin, Zombie Lupin, Copper Drake, Lunar Pixie,
Lv51-55: Lupin, Zombie Lupin, Copper Drake, Lunar Pixie, Jr Yeti, Croco, Stone Gollem
Lv56-65: Jr Yeti, Croco, Stone Gollem, Coolie Zombie, Miner Zombie
Lv66-70: Jr Yeti, Hector, Coolie Zombie, Dark Stone Gollem, Tauromacis
Thief (Bandit)
Lv30-35: Bubbling, Jr Neki, Horned Mushroom, Jr Sentinel, Zombie Mushroom, Wild Boar, Alligator
Lv36-40: Bubbleing, Blue Mushroom, Horned Mushroom, Zombie Mushroom, Evil Eye, Alligator
Lv41-45: Evil Eye, Fire Boar, Alligator, Jr Cellion, Jr Grupin, Jr Liona, Star Pixie, Jr Pepe, Cursed Eye, Copper Drake
Lv46-54: Star Pixie, Jr Pepe, Curse Eye, Zombie Lupin,
Lv55-60: Lupin, Zombie Lupin, Cold Eye, Wild Cargo
Lv61-65: Coolie Zombie, Miner Zombie, Cold Eye, Lunar Pixie, Clang, Sun Pixie, Tauromacis
Lv66-70: Hector, Coolie Zombie, Miner Zombie, Cold Eye, Lunar Pixie, Umti, Sun Pixie, Tauromacis
Wizard (Fire)
Lv30-35: Horned Mushroom, Jr Sentinel, Zombie Mushroom, Evil Eye, Jr Wraith, Ice Sentinel (35)
Lv36-40: Zombie Mushroom, Evil Eye, Sentinel, Ice Sentinel, Jr Grupin, Jr Wraith*
Lv41-45: Leatty, Jr Grupin, Jr Pepe, Jr Wraith, Cold Eye
Lv46-50: Jr Pepe, Jr Wraith, Cold Eye, Nependeath
Lv51-60: Nependeath, Jr Yeti, Grupin
Lv61-70: Jr Yeti, Jr Yeti (Growth), Pepe
Wizard (Poison)
Lv30-35: Horned Mushroom, Jr Sentinel, Zombie Mushroom, Evil Eye
Lv36-40: Zombie Mushroom, Evil Eye, Sentinel, Jr Wraith
Lv41-45: Sentinel, Leatty, Jr Wraith, Alligator, Dark Leatty
Lv46-50: Alligator, Leatty, Dark Leatty
Lv51-60: Alligator, Croco
Lv61-70: Jr Yeti, Yeti, Werewold (68-70)
Wizard (Ice)
Lv30-35: Horned Mushroom, Jr Sentinel, Zombie Mushroom
Lv36-40: Zombie Mushroom, Fire Boars, Ligators (Not recommended)
Lv41-45: Fire Boars, Ligators (Not recommended), Jr. Cellion
Lv46-50: Fire Boars, Ligators (NR), Jr. Cellion, Jr. Wraiths, Copper Drakes
Lv51-60: Jr. Cellion, Jr. Wraiths, Curse Eye, Cellion, Copper Drakes, Fire Drakes (60)
Lv61-70: Cellion, Liona, Cooli Zombie (57), Miner Zombie (57), Fire Drake (60)
Wizard (Lightning)
Lv30-35: Horned Mushroom, Zombie Mushroom, Evil Eye
Lv36-40: Zombie Mushroom, Fire Boar, Evil Eye, Lorang
Lv41-50: Jr. Cellion, Jr. Grupin, Jr. Wraiths, Lorang, Copper Drakes
Lv51-55: Jr. Cellion, Jr. Grupin, Jr. Wraiths, Curse Eye, Lorang, Copper Drakes
Lv56-70: Zombie Lupin, Coolie Zombie (70), Miner Zombie (70)
Cleric
Lv30-40: Horned Mushroom, Wild Boar, Zombie Mushroom, Evil Eye, Jr. Wriaths (35)
Lv41-50: Zombie Mushroom, Evil Eye, Zombie Lupin
Lv51-70: Jr. Wraiths, Zombie Lupin, Wraiths (48), Coolie Zombie (57)
NOTE* Sorry Clerics, you'll be seeing a LOT of these monsters continuously until they implement Ludibrium which will bring in a lot of new Undead monsters. If you want to see variety, I suggest you find a Warrior friend to party with.
Hunter
Lv30-35: Horned Mushroom, Jr Sentinel, Wild Boar, Zombie Mushroom
Lv36-40: Wild Boar, Evil Eye, Fire Boar, Ligator, Jr. Cellion, Jr. Grupin, Jr. Liona
Lv41-55: Fire Boar, Ligator, Jr. Cellion, Jr. Grupin, Jr. Liona, Lupin, Zombie Lupin, Stone Gollem
Lv56-60: Stone Gollem, Jr. Yeti, Hector
Lv61-70: Jr. Yeti, Hector, Coolie Zombie
Crossbowman
Lv30-35: Horned Mushroom, Jr Sentinel, Wild Boar, Zombie Mushroom
Lv36-40: Wild Boar, Evil Eye, Fire Boar, Ligator, Jr. Cellion, Jr. Grupin, Jr. Liona
Lv41-50: Fire Boar, Ligator, Jr. Cellion, Jr. Grupin, Jr. Liona, Lupin, Zombie Lupin, Stone Gollem
Lv51-60: Cellion, Grupin, Liona, Stone Gollem, Jr. Yeti, Hector
Lv61-70: Jr. Yeti, Hector, Coolie Zombie