Here's the list of concept art Pokémon:
-Furfrou
-Blastoise
-Machamp
-Wingull
-Wobbuffet
Part of the hotel decoration:
-Horsea
-Staryu
-Spheal
-Chinchou
-Magikarp
-??(Krabby)
Part of the food locale logo:
-Slaking
Edit 1(10th March 2016): Recent Japanese trailer shows Meowth:
https://www.youtube.com/watch?v=2r0_F-_ClcQ
Edit 2(2nd June 2016):
https://www.youtube.com/watch?v=XW14HO7C1Dg
Gengar and Salamence have been shown. Rotom exists in Rotom Pokédex.
https://www.youtube.com/watch?v=5K3Cs7WyAxE Luvdisc!
https://www.youtube.com/watch?v=T6N09Ak3q94 Slowpoke!
http://www.pokemon-sunmoon.com/en-us/discover-pokemon-using-the-qr-scanner/ QR scanner artwork shows Serperior, Medicham and Dunsparce. In-game image shows Pikachu.
Edit 3(5.06.2016): Luvdisc's video also contains Corsola.
Edit 4(11.06.2016):
https://www.youtube.com/watch?time_continue=31&v=l7cW0F4JMsc Zygarde 10% and Metagross.
https://www.youtube.com/watch?time_continue=46&v=ZeZ_8s_kWXg Zygarde 10%, Complete Zygarde and Garchomp.
Edit 5(14.06.2016):
https://www.youtube.com/watch?v=9Ojd6FzTaEM New trailer shows Magearna battling against Krookodile and Pangoro with Eevee. Pikachu is seen again in Battle Royale.
https://www.youtube.com/watch?v=fKVHOk7KM_g The E3 stream showcased Pichu, Pikachu, Caterpie and Ledyba. Battle Royal area features Haxorus, Tyranitar, Charizard and Gyarados.
Edit 6(30.06.2016):
https://www.youtube.com/watch?time_continue=190&v=NTt65qAkR84
New Japanese trailer shows Fearow,
Pidgeotto Spearow, Flygon, Milotic, Slowbro, Kangaskhan, Pancham, Emolga, Zygarde 50%, Dragonite. Zygarde 50% can Swarm Change into Zygarde Complete.
Edit 7(01.07.2016):
http://www.pokemon-sunmoon.com/en-us/a-sneak-peek-at-new-features/
Stoutland is seen as a rideable Pokémon.
http://www.pokemon.co.jp/ex/sun_moon/collect/160701_01.html
Zubat, Psyduck, Riolu and Klefki are confirmed for Kalos dex, and Pikachu-line is shown alongside them.
http://www.pokemon.co.jp/ex/sun_moon/grow/160701_01.html
Gible-line is shown for evolution graphic.
Edit 8(03.07.2016):
https://www.youtube.com/watch?v=RHS0DjTw5ho
Hong Kong trailer features Arcanine and Electabuzz.
Edit 9(07.07.2016):
https://www.youtube.com/watch?v=LJ2sin-c3Kk
Salandit trailer showcases Skarmory, and reshowcases Zubat.
Edit 10(13.07.2016):
https://www.youtube.com/watch?v=TyIkvadJU1Q
Fletchling, Butterfree, Poliwag, Lillipup, Kangaskhan, Eevee, Umbreon, Pancham, Tauros, Sharpedo, Lapras are showcased in the latest trailer.
Edit 11(19.07.2016):
https://www.youtube.com/watch?v=hN2e93vlYvI&feature=youtu.be
Japanese trailer showcases Murkrow, Snorlax, Sylveon, Machamp, Tauros, Ariados.
https://www.youtube.com/watch?time_continue=135&v=vKosBJ1Uko0
English trailer reshowcases Pangoro.
Edit 12(01.08.2016):
https://www.youtube.com/watch?time_continue=314&v=3AZHowhxM0U
New trailer showcases Charizard and Masquerain. Known Alola forms include Sandshrew, Sandslash, Exeggutor, Vulpix and Ninetales. English trailer also shows Dragonite, Bagon, Salamence, Fearow, Delibird, Nosepass.
https://www.youtube.com/watch?v=Iaav6J6XzFs
Japanese trailer showcases Lapras, Trevenant, Miltank, Lucario, Politoed, Primeape, Psyduck, Gigalith, Lillipup, Sudowoodo, Rufflet, Goodra, Shelgon, Archeops, and regular Exeggcute. Popplio attacks a Flareon. Rowlet attacks a Carbink, but only its name is displayed. Edit:
Here's the pic.
http://www.pokemon-sunmoon.com/en-us/aug-1-captains/
Sophocles has an Electrode keychain, and Kiawe has a Marowak.
Edit 13(11.08.2016):
https://www.youtube.com/watch?v=7VmMURRKWFk
New Japanese trailer showcases Magnezone, Drowzee, Haunter, Trubbish, Pinsir, Hariyama, Leafeon and regular Cubone. It also reshowcases Gengar, Ariados, Pikachu and Golbat.
https://www.youtube.com/watch?v=Py2LxgWBaRQ
Gyarados, Electivire, Phantump, Weavile and Aerodactyl has been showcased by the English trailer. It also reshowcases Zubat, Machamp, Metagross.
Edit 14(12.08.2016):
http://www.pokemon.co.jp/ex/sun_moon/pokemon/
Dragonite and Zubat lines are confirmed to be in the game, retaining their original forms.
Edit(18.08.2016):
https://www.youtube.com/watch?v=SFWLoyZESAc
Turtonator's trailer showcased Torkoal, Tirtouga and Carracosta.
Edit (19.08.2016):
https://www.youtube.com/watch?v=-1hsh267tUM
Shellder appears in the most recent trailer, alongside reappearances of Gengar, and Pancham.
Crabrawler's Worlds video:
https://www.youtube.com/watch?v=onBpM9QPyyY
Shows Crabrawler using Dynamic Punch, Close Combat, Stone Edge, an unidentified move and Crabhammer.
Kangaskhan, Smeargle, Talonflame, Cresselia, Landorus Therian and Ferrothorn are shown.
Edit(26.08.2016):
http://www.takaratomy.co.jp/products/pokemon/moncolle_get/index.html
Moncolle GET figures show Rowlet, Pikachu, Turtonator, Lucario, Snorlax, Garchomp, Rowlet, Litten, Salandit, Bewear, Charizard, Magmortar and Bounsweet.
Edit(01.09.2016):
https://www.youtube.com/watch?v=CsTuHGpLJfM&feature=youtu.be
Recent trailer showcases Munchlax and Alolan Rattata, and reshowcases Aerodactyl, Alolan Raichu, Munchlax, Caterpie and Gumshoos.
https://www.youtube.com/watch?v=Rt-4Hef90VA
Japanese trailer showcases Ditto, Munchlax and Alolan Rattata, and reshowcases Gyarados, Alolan Raichu, Zubat.
Edit(06.09.2016):
https://www.youtube.com/watch?v=YR1ssSZfoGY
Drifloon is Sun exclusive, Misdreavus is Moon exclusive.
Pelipper appears.
Poliwhirl appears. Riolu appears.
Wigglytuff, Happiny, Bastiodon, Alakazam, Granbull are new.
Edit(09.09.2016):
http://www.serebiiforums.com/showth...OST-POKEMON-NEWS-HERE&p=18178574#post18178574
Golduck confirmed to be in its regular form.
https://www.youtube.com/watch?v=8oO_P4GX_RA
Starmie and Hypno are shown.
Edit(20.09.2016):
https://www.youtube.com/watch?v=yhNJ7pX12Tw&feature=youtu.be
Poliwrath, Chansey, Parasect, Scyther, Magmar appears in Japanese trailer.
https://www.youtube.com/watch?v=m8lfI66T5II&feature=youtu.be
Cloyster appears in English trailer.
Edit (04.10.2016):
Japanese trailer showcased Swablu, Shroomish, Seaking and Magneton models.
Icons will be discussed below.
https://www.youtube.com/watch?v=n9o552CaJV8&feature=youtu.be
Japanese:
Poké Pelego: Rockruff, Pelipper, Spearow, Lurantis, Butterfree, Salandit, Cutiefly, Pikachu, Orocorio Pom Pom, Bonsly, Caterpie, Machop, Crabrawler, Eevee, Wishiwashi, Pikachu(again), Petilil, Hariyama, Parasect, Rockruff (again), Bonsly (again), Alolan Rattata, Alolan Exeggutor, Golbat, Pichu, Psyduck, Staryu, Butterfree (again), Pikachu(again), Butterfree (again), Metapod, Gastly, Carbink, Finneon, Pikachu, Machop (again), Staryu (again), Charjabug, Eevee (again).
GTS: Cleffa, Pikachu, Pichu, Clefairy, Staryu, Fletchinder, Feebas, Happiny.
https://www.youtube.com/watch?v=ciqAkdXQ9dw
English:
Poké Pelego: Magikarp, Pikipek, Yungoos, Slowpoke, Alolan Meowth, Orocorio Pom Pom, Salandit, Finneon, Staryu, Absol, Pyukumuku, Passimian, Crabrawler, Passimian (again), Togedemaru, Lycanroc Midday, Mudsdale, Fomantis.