In my opinion, the best junglers are not only strong early, but are also effective late game.
For this reason, I would place the following champions in a "tier 1" type bracket:
These are the lesser, "tier 2" junglers, who are not effective throughout the game:
Maokai: Strong early (excellent ganks), turns into support/tank late game; doesn't really do any late game damage
Amumu: Fairly weak early until gets level 6, fairly vulnerable to countering, clears fast, turns into support/tank late game
Malphite: Very Strong mid game (~levels 6 -12) turns into tanky initiator/support late game
Shaco: Strong early and mid game, but very squishy and almost ignorable in most games after about 15 minutes
I can continue this list, but I won't go into detail on all the champions. Sejuani, Alistar, and Nautilus also fit here, and a few others, including Cho'Gath and Shen.
The "tier 3" junglers are mostly champions that would be better off in a different role.
I'm going to place Yi here, along with Warwick. Both are better solos than junglers, given their needs for farm, and Warwick's insane ability to sustain in lane.
Hope I gave you something to go off of