Oh, nonsense. You mentioned Kecleon in your question and in the tag, so I thought I could show you that Kecleon can be good in the right situations. Just don't give it Color Change, silly. :)
Geico (Kecleon) (M) @ Assault Vest
EVs: 252 HP / 80 Atk / 176 SpD
- Aqua Tail
- Drain Punch
- Power-Up Punch
- Sucker Punch
Since he gets STAB from every move, Drain Punch is now a pretty nice move, allowing him to live longer. Sucker Punch gets that nice priority, Power-Up Punch makes up for what little attack he has, and Aqua Tail is coverage.
Now, I would never recommend using him any higher than NU. His viability wears out kinda quickly. But it's fun to mess with people on this set. As soon as someone powers up a Psychic move, you Sucker Punch them (no matter how effective). In fact, you could do this for Aqua Tail as well. Sucker Punch works as a sort of defense mechanism.
On to your real question: The list Fizz has given you sums it up mostly. And he's right, there are some surprising additions on there. Several of them have potential for use in low-end tiers like NU and PU. Some of my favorites of those include Ampharos, Electivire (!?), Crustle, Gorebyss, Huntail, and Trevenant; however, the vast majority have almost nothing. Several have usable, viable stat pools or movepools, but nothing else to supplement it, and thus they are inferior to other choices. Electivire in particular once was listed as high as UU, but it's taken a steep fall since Gen 5.