Abomasnow
Without Stealth Rock, and with free switching, Hail teams just got a whole lot better. Expect Abomasnow leads to be very common. Furthermore, if things look bad Abomasnow doesn't even need to stay in a single turn; go immediately to Rotom-F and start killing things. And it is of course slower than Ninetales or Groudon- Abomasnow will be getting Hail up. Quiet can minimize speed and exploit Blizzard, or you could have a SubSeeder.
Groudon
Sets up Sun. Furthermore, the ability to bring a +2 Groudon back into play is ridiculous.
Rayquaza
Cancels out weather, avoids Stealth Rock, fairly fast, with two huge attack stats for sweeping. Doesn't even have bad bulk.
Heatran
It's Heatran. Only now it's in the sun, and can dodge Earthquakes for Moltres. Yay?
Yanmega
Hypnosis, Tinted Lens, and a diverse movepool makes this thing terrifying without worry of Stealth Rock. Furthermore, Speed Boost is absolutely abusable.
Urgamoth
This is scary in Singles. In Rotation Battle, where it can leave without losing Butterfly Dances and doesn't have to deal with Stealth Rock? It'll be an absolute monster.
Ho-Oh
130 base Attack, STAB Sacred Fire/Brave Bird, and scary defensive ability. Without being neutered by Stealth Rock. This thing is nuts.
Rotom-H
Should return to its status as the premiere Scizor counter and a killer wall, without SR damage on its limited HP. Spinblocking isn't really an issue when there are no hazards worth a damn.
Reshiram
150 base SpA. STAB Blue Flame, essentially a super Fire Blast, and Draco Meteor. Scary.
Regice
Still lacks recovery, but with SR gone and the ability to switch in and out without losing a turn, Regice just got a whole lot better. 80/100/200 defenses are nuts.
Weavile
Weavile can now exit battle freely and avoid Stealth Rock, making it far less easily counterable. Its movepool could still be better, though...
Rotom-F
100% accurate STAB BoltBlizzard+bulk=insanity
Articuno
The only reasons this birdie isn't everywhere, Calm Minding, soaking up hits, and Roosting off damage, are Stealth Rock and difficulty coming in. Both of these are nullified.
Jynx
115 SpA, STAB Blizzard, decent Speed, and a STAB sleep move. Yikes.
Walrein
Stallrein is an asshole, and with no Stealth Rock it's even more of an asshole. Furthermore, it has a Fire neutrality Hail teams will need. I could also see a Sleep Talker with Thick Fat to soak up Fire moves from things like Reshiram that enjoy Hail.
Glaceon
The game's strongest Blizzard, tied with Kyurem, Ice Body, and good bulk make this thing very very scary.
Kyurem
This thing does it all. 130/130/90 offenses and 125/90/90 defenses. Soaks up hits, breaks down walls with a mixed set, or makes a fantastic Scarfer with Blizzard and Dragon Pulse. Draco Meteor is less viable in Rotation play, though.
Arceus
Ice/Fire forms are perfect for either a Hail or Sun team. It's fast, absurdly powerful, and bulky as hell. Also, it can maintain its Calm Minds when leaving play!
Moltres
125 base SpA, decent Speed, and STAB Fire Blast/Air Slash.
In the sun, this thing is amazing.
Archeos
No SR means it comes in without being neutered by a min SpA Blissey's NFE Flamethrower.
Vultina
Huge defenses. Roost. Decent defensive typing. Dust-proof letting it fit on Hail teams. Tailwind to support slow sweepers like Glaceon. The 100% accurate, no longer easily canceled Fake Tears. This will be a top-notch supporter with a Tailwind/Fake Tears/Roost/Dark Pulse set. Fake Tears, Tailwind, switch to a Special sweeper.