Level(Buy maplestory mesos) 60-64: Red Drakes, Hot Sands, Helios Tower, the old spots. You can TRY to train at Buffoons if you like, but that's not generally a good idea. If you are not so obsessed with big damage, electrifying some jr. Yetis may not be a bad idea, as with freezing up some hectors and zombies.
Level(MapleStory powerleveling) 65-70: go to Mystic Path 3 (mp3) in Singapore if your version has it. Level 70-75: Same old, same old. Zombies, Hot Sands, Red Drakes. Buffoons might be more practical to hunt right now, but there is not much change in training. If you are still doing RETZ, you must be a masochist.
Level 76-83 in Maplestory: IS mages can start killing Death Teddies now, since there are some sniping points present where you can hit them without worrying about getting hit. It's not great on your wallet, but it's very fast training. If you need money, Zombies are your friend again. You can also try Buffoons. Comp Mages should just stay at Zombies or Buffoons right now.
Level 83-88: IS mages got some options now. Bains are a pain to get to and there are not many sniping spots, but they are like Death Teddies with more money, though the map is not pure Bains and poison geysers are annoying. Death Teddies are as good as always. If you feel bold, you can try Vikings. Comp mages should probably go for Bains now, or Vikings if you are bold.
Level 88+: Vikings are a great target. JMSers could probably go for Bains in Weapon Storage, the map after Anego or try the Kentauruses which give good exp. Leafre though we are not sure about their spawns.