Apparently everyone just up and forgot about this, so I'm going to have to bump it up.
Again, I really don't want to make my votes until I see some other people's opinions on this. However, if I must get the ball rolling myself, I will.
Sableye: Yes Sure it has trouble with a few Pokemon, but so do all the Pokemon on this list. For the most part, stall is wrecked by the little ghost, and I know from experience it can full counter entire stall teams. Definitely tier 1.
Jellicent: No It's just too slow to function completely as a stallbreaker. Unless you're going to run some crazy fast spread, it simply won't be able to beat faster defensive Pokemon, as they'll recover or toxic Jellicent while it attempts to taunt them again. And there are just too many faster defensive Pokemon to fit Jellicent into Teir 1.
Reuniclus Yes Sure it gets phazed, but eventually when it comes down to last Pokemon, it will demolish them all. Oh sure, Perish song puts a dampner on it, but like, how many Pokemon get that in OU? Two? That's not enough to devalue Reuniclus on its own.
Mew: Yes Unlike Jellicent, it IS fast enough with its base 100 speed, and it has better stats overall to boot. Sure its typing means it can't wall as well, but we're talking breaking walls here, not being them.
Gliscor: No It would if it weren't for the existence of rain stall, which shits all over Gliscor like nothing else. Rain boosted Scalds are just too much for the bat to handle. It comes close but when an entire branch of stall kills you, you just don't make the cut for Teir 1.
Sigilyph: Yes Same boat as reuniclus, only with the added threat of dark types. With only one dark type in OU that could be considered a wall though (Tyranitar), it's not enough to hold Sigilyph back.
Breloom: Abstain I really want to hear some opinions of others on this one first.
Deoxys-D Yes Should you chose to use a stallbreaking set, I doubt there'd be anything more effective out there at doing it. It's just that people usually can't pass up its ability to set up screens and hazards.
Whimsicott No Tried it recently and was greatly underwhelmed. Too many grass types to screw it up, Leech seed is too easily avoidable, and it just doesn't have the stats or typing to pull it off.
Espeon No Morning Sun's low PP is what settles it. It might be able to deal with one wall fairly easily, but Espeon will just get worn down too quickly to stick around the whole match. Most special walls can beat it too by simply attacking it, and if inclement weather is up, it's definitely not going to last long.
Xatu Yes Ironically, while its OU sibling Espeon doesn't make the cut, Xatu does. Xatu's more reliable recovery in Roost seals the deal, allowing it to beat pretty much any wall given enough time and it actually has the ability to do it more than once. Just don't expect it to fare quite as well against offensive mons.
Mandibuzz Abstain I just don't know enough about the bulky bird to call it.
Wobbuffet No One of the key factors in being Tier 1 is the ability to stallbreak without support. The problem is of course that Wobbuffet requires a LOT of support to break down walls. It can't usually do it more than once per a match either, due to its lack of recovery. Unless you support it of course, but that brings back the first problem.
Jirachi Abstain Too on the fence. The fact it's vulnerable to phazing and spikes works against it, but immunity to toxic, healing and Calm Mind all work for it. I'm not convinced its as effective a last mon as Reuniclus is, but it could fit the bill. It's trouble with Heatran, Hippowodon, and Gliscor work strongly against it though.