Yeah, the Dark/White Hoxes and the Bahemeth-y dudes (forget what they're called, begins with a "G") are really great for leveling, starting around 72 or so. Just run around the lake with the interconnected platforms, and beat up on 3 or so at a time.
Unfortunately, it's a bit difficult to find good grinding spots after level 75. There are some biggies in the Bionis Interior that become fairly manageable, but they're spread out, and not fast for leveling. There's one cove in Eryth Sea that's home to some monsters that are perfect for mid-70s, but you have to swim to get there. I think it's north of the Ether Windfarm. But it is weird, the game doesn't have an innordinate number of level 70-85 monsters. Suddenly, there's TONS for high 80s, 90s, and some really obvious 100s (Dinos, Snow Giants, etc), but there's a big gap in there that I never bothered getting through. I beat the game at 81, so I never got high enough to start smashing greater Telethia, Fire Ants, Giants, etc. I searched high and low for good high-70, low-80 monsters to grind on, and I just don't think there are any.
Hint: some early areas actually change after certain events take place late in the game. There are new high level monsters in the easy dungeons. But once again, Level 85+, though I'm not sure I went back through EVERY early dungeon.