Ok, so Clerics are pretty useful. They remove status from the team to somewhat give them new life.

Here is a list of pokemon with the movepool allowing them to be a Cleric:

+ Blissey
+ Lapras(XD)
+ Miltank
+ Granbull
+ Altaria(XD)
+ Articuno(XD)
+ Delcatty
+ Dragonite(XD)
+ Chimecho
+ Vileplume
+ Roselia
+ Parasect
+ Smeargle
+ Lickitung(Box/NYPC)
+ Celebi

That is a pretty big list however not all of these pokemon are fit for utilizing the the cleric style effectively. Out of that list, these are the most apt to the job:

+ Blissey
+ Lapras
+ Altaria
+ Celebi
+ Miltank
+ Granbull

Many people go with Blissey due to that ungodly HP and great Sp.Def, allowing it to make an easy switch into a special attack and amora/bell on their switch. Celebi is also a common choice because who would want an evil little onion on their team? Miltank has its own analysis. However there are good points to the others.

Lapras (M) @ Leftovers
Trait: Water Absorb
EVs: 12 HP / 176 Def / 252 SAtk / 68 SDef
Modest Nature (+SAtk, -Atk)
- Heal Bell
- Ice Beam
- Rest
- Thunder(bolt) / Surf / Hydro Pump

I was slim on the HP because of the fact that it has a high amount with small defense. Ice Beam gets STAB and can hit 4x on a lot of things. Thunder has a para-chance and Rest gives that chunk of HP back.

Because of Water Absorb, and a nice times 4x Ice Resist, this thing LOVES water types like Milotic and Vaporeon. Switch into one of those then Bell on their switch. Simple as pie.

Altaria (M) @ Leftovers
Trait: Natural Cure
EVs: 180 HP / 96 Spd / 124 SAtk / 108 SDef
Calm Nature (+SDef, -Atk)
- Heal Bell
- Rest
- Dragon Claw
- Roar / Sleep Talk / Haze

This is a blissey with grass and fire resist along with some sleek Sp.Def minus the HP. Dragon Claw is there purely for the sake of an Attack and STAB. Natural Cure makes Rest better than toilet paper and Heal Bell is a no-brainer.

As long as you steer clear of Ice attacks this thing can run with the best of them. Throw in a well placed Bell then switch way. Sleep Talk helps make it a reusable Sleep Absorber as well as allowing it to Cleric while sleeping.

Granbull (M) @ Leftovers
Trait: Intimidate
EVs: 60 HP / 252 Atk / 196 Def
Adamant Nature (+Atk, -SAtk)
- Bulk Up / Thunder Wave
- Physical Attack
- Physical Attack
- Heal Bell

I love this guy's movepool. T-wave can help with speed support for the team while Bulk Up can be just plain scary. Its already decent Def combined with Intimidate allow it to switch more smoothly into physical attacks. Heal Bell can be thrown around like random almost because of its physical endurance and Thunder Wave.

Couple it with a Wisher and you're set for a full time beller.

I'm not to versed in UU or NU so someone else can handle those pokemon suited for Clerics in those formats.

Notable Points:

+ Blissey makes a GREAT Ubers Cleric. Celebi would be a bad decision because Psychic pokemon have to face off with every Dark, Ghost, and Bug attack imaginable.

+ DD Lapras with Heal Bell can put the hurt on Blissey/Snorlax.

You forgot that Ampharos gets Heal Bell in XD. And Celebi's not a bad beller really, as it can pull off a Heal Bell in time to get in and out. I know because I've used it constantly. But whether this is contradictory or not, it's not as good a cleric as some of the other choices.

Celebi has a good typing and an above average base in all stats. Natural Cure, Recover, Leech Seed, Calm Mind, and the potential for 101 Subs. How is it not as good as the others? It isn't one of the most annoying pokemon ever created for nothing.

True Amphy is a Beller..it doesn't help it too much however. Bell, FP, TBolt, HP:Ice/FirePunch is about the best I can see. Its trait, Static, isn't too supportive of that strat either.

The Best Clerics, imo, are Lapras, Blissey, and Celebi. Lapras is a hot bulky water with a pretty variable movepool. Blissey is just LOL @ special attacks. Celebi is an annoying pixie onion from the gaping pits of the underworld. All 3 are my favorites to Heal Bell.

For Lapras why not put sing into the moveset? That way, your opponent either switches when you do or they leave a sleeping pokemon in the battle.

Sing > what, though. The logic makes sense...just finish the thought I guess.