I'm not completely sure if this is worth a thread, but sure, why not.
Skarmory and Blissey are still very very common, so your statement isn't that correct, but thuth to be told, they are dropping little by little. Most Stall teams have Blissey, but not always Skarmory in it. Skarmory has it's pros and cons, though there are others, with their pros and cons as well. Forretress is the prime contender, of course.
I've made a list of most of todays popular stall Pokemon (excluding Blissey, whixh needs no explanation imo):
Hippowdon has astronomical Defense and useful SpD as well, making it and few others a worthwile non-Outrage Mixmence counter with heavy SpD investment, while still countering Tyranitar like no other. Roar and Toxic, not frgetting SR still making this guy worthwile in any stall team, and it's main attraction is actually the ability to put SS up for the rest of the match. All of these make Hippowdon a very very capable and popular Pokemon on stall teams.
Forretress is one of the few Pokemon that can set up both Spikes and Toxic Spikes (and spin them away), so it is self-explanatory why it is popular on stall teams. The thing that makes it so attractive above other like him is his typing and stats though - HP and Def that toghether are bigger then Skarmorys, as well as neutrality to Thunderbolt make Forretress a worthwile competitor to Skarmorys spot as a Spiker on a stall team, with the only letdown being a 4x Fire weakness and no reliable recovery.
Suicune doesn't have the ability to set up entry hazards nor spin them away, but the combination of its bulk, ability and typing make it a force to be wary of. 115 base Def and SpD make it an amazing sponge, while Pressure makes it win against other CM sweepers in a stall battle. The CM sets are of course the prime attraction, being able to rip apart teams after a few CMs. The lack of recovery hurts though. Roar and Ice Beam are also attractive.
Suicune's defenses helps it check and counter an amazing amount of threats, and like Hippowdon, can stop Mixmence to an extent. All of these make Suicune a great addition to stall teams.
And we get to Skarmory. Roost, Spikes and Whirlwind are huge assets to stall teams, and so Skarmory is always a very worthwile option. Taunt, BB and typing is merely a plus. Typing, as well as stats make Skarmory an amazing Pokemon, being able to counter a lot of common physical sweepers. Though a lot of Pokemon out there lurk and take care of Skarmory easily, other Pokemon (caugh Blissey caugh) can take care of them.
Celebi's movepool is the main catch here - Perish Song, Baton Pass, STAB Grass Knot, Recover, Calm Mind, Swords Dance - the list goes on! Celebi can always find itself a roll in stall teams, be it to stop a last-Pokemon sweep with PS, Baton Pass to a teammate or just to check and cointer threats such as CursePert, Gyarados and more. It can also be an excellent lure to Scizor, carrying HP Fire and enough EV investent to take it out in a hit. Base 100 stats across the board justify Celebi's ability to take on almost every roll.
Rotom-A is the primary spin blocker in todays metagame, mostly because of it's Electric typing, giving its team access to Electric-STAB, along with excellent stats, wit hacceptable SpA and defenses. Each form also has a unique move to abuse. Checking and countering a lot of threats easily, such as Metagross, Jirachi and more make it that more attracting.
Latias acts somewhat like Suicune, only with less defences but better typing (to an extent) and Dragon STAB, not to mention base 110 speed and a bigger movepool, allowing it to check multiple threats such as Heatran and Mixmence while being able to sweep with CM. Recover is also a huge plus, and Latias has a lot of other trickes up her sleve such as Refresh, Psycho Shift and more.
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I think that this is enough for now. The stall team's slots have a lot of options as you can see, and a lot of combinations can be made. It mostly comes down to overall resistances in the end, after counters to the majority of the metagame, a hazard layer(s), a rapid spinner and a spin blocke are there, most of the time.
Edit: Oh, sorry about that. Maybe the fact that I didn't play competitive Pokemon back in RSE had an effect. Anyway, this is really a very short list. There are many other options such as Tentacruel, Dusknoir, Spiritomb, Zapdos, Jirachi and many more. To compile a list like that, I would need much more time.