Confirmed Alola Pokédex so far:

New Species:

1. Rowlet
2. Dartrix
3. Rowlet 2
4. Litten
5. Torracat
6. Litten 2
7. Popplio
8. Brionne
9. Popplio 2
10. Pikipek
11. Pikipek 1
12. Pikipek 2
13. Yungoos
14. Gumshoos
15. Rockruff
16. Lycanroc
17. Komala
18. Komala 1
19. Grubbin
20. Charjabug
21. Vikavolt
22. Drampa
23. Bruxish
24. Cutiefly
25. Ribombee
26. Togedemaru
27. Salandit
28. Salandit 1
29. Stuffull
30. Bewear
31. Mimikyu
32. Wimpod
33. Wimpod 1
34. Bounsweet
35. Steenee
36. Tsareena
37. Comfey
38. Mudbray
39. Mudsdale
40. Minior
41. Fomantis
42. Lurantis
43. Oricorio
44. Sandygast
45. Palossand
46. Wishiwashi
47. Pyukumuku
48. Crabrawler
49. Morelull
50. Morelull 2 
51. Turtonator 
52. Jangmo-o
53. Hakamo-o
54. Kommo-o
55. Type: Null
56. Silvally
57. Passimian
58. Oranguru
59. Tapu Kako
60. Solgaleo
61. Lunala
62. Magearna

Ultra Beasts:

1. UB-01 ???
2. UB-02 Beauty
3. UB-02 Absorption

Alolan Form:

1. Exeggcute (Regular)
2. Exeggutor
3. Vulpix
4. Ninetales
5. Sandshrew
6. Sandslash
7. Meowth
8. (Persian)
9. Cubone (Regular)
10. Marowak
11. Pichu (Regular)
12. Pikachu (Regular)
13. Raichu 
14. Rattata
15. Raticate
16. Grimer
17. Muk

Old Species:

1. Charmander
2. Charmeleon
3. Charizard
4. Caterpie
5. Metapod
6. Butterfree
7. Furfrou
8. Squirtle
9. Wartortle
10. Blastoise
11. Machop
12. Machoke
13. Machamp
14. Wingull
15. Pelipper
16. Wynaut
17. Wobbuffet
18. Horsea
19. Seadra
20. Kingdra
21. Krabby
22. Kingler
23. Spheal
24. Sealeo
25. Walrein
26. Chinchou
27. Lanturn
28. Magikarp
29. Gyarados
30. Slakoth
31. Vigoroth
32. Slaking
33. Meowth
34. Persian
35. Gastly
36. Haunter
37. Gengar
38. Bagon
39. Shelgon
40. Salamence
41. Luvdisc
42. Corsola
43. Slowpoke
44. Slowbro
45. Slowking
46. Beldum
47. Metang
48. Metagross
49. Gible
50. Gabite
51. Garchomp
52. Sandile
53. Krokorok
54. Krookodile
55. Pancham
56. Pangoro
57. Eevee
58. Leafeon
59. Jolteon
60. Glaceon
61. Sylveon
62. Flareon
63. Espeon
64. Umbreon
65. Vaporeon
66. Ledyba
67. Ledian
68. Spearow
69. Fearow
70. Feebas
71. Milotic
72. Trapinch
73. Vibrava
74. Flygon
75. Kangaskhan
76. Dratini
77. Dragonair
78. Dragonite
79. Emolga
80. Lillipup
81. Herdier
82. Stoutland
83. Zubat
84. Golbat
85. Crobat
86. Riolu
87. Lucario
88. Psyduck
89. Golduck
90. Klefki
91. Growlithe
92. Arcanine
93. Elekid
94. Electabuzz
95. Electivire
96. Skarmory
97. Fletchling
98. Fletchinder
99. Talonflame
100. Poliwag
101. Poliwhirl
102. Poliwrath
103. Politoed
104. Carvanha
105. Sharpedo
106. Lapras
107. Tauros
108. Miltank
109. Murkrow
110. Honchkrow
111. Munchlax
112. Snorlax
113. Spinarak
114. Ariados
115. Surskit
116. Masquerain
117. Delibird
118. Nosepass
119. Probopass
120. Phantump
121. Trevenant
122. Mankey
123. Primeape
124. Roggenrola
125. Boldore
126. Gigalith
127. Bonsly
128. Sudowoodo
129. Rufflet
130. Braviary
131. Goomy
132. Sliggoo
133. Goodra
134. Archen
135. Archeops
136. Carbink
137. Trubbish
138. Garbodor
139.  Magnemite
140. Magneton
141. Magnezone
142. Drowzee
143. Hypno
144. Pinsir
145. Makuhita
146. Hariyama
147. Sneasel
148. Weavile
149. Aerodactyl 
150. Torkoal
151. Tirtouga
152. Carracosta 
153. Shellder
154. Cloyster 
155. Ditto 
156. Igglybuff
157. Jigglypuff
158. Wigglytuff
159. Happiny
160. Chansey
161. Blissey
162. Snubbull
163. Granbull
164. Shieldon
165. Bastiodon
166. Drifloon (Sun)
167. Drifblim (Sun)
168. Misdreavus (Moon)
169. Mismagius (Moon) 
170. Abra
171. Kadabra
172. Alakazam
173. Magby
174. Magmar
175. Magmortar
176. Paras
177. Parasect
178. Scyther
179. Scizor
180. Swablu
181. Swablu
182. Altaria
183. Shroomish
184. Breloom
185. Goldeen
186. Seaking
187. Petilil
188. Lilligant
189. Finneon
190. Lumineon
191. Cleffa
192. Clefairy
193. Clefable

Status unknown but confirmed:

1. Cubone
2. Marowak

Miscellaneous:

1. Dunsparce
2. Meditite
3. Medicham
4. Snivy
5. Servine
6. Serperior
7. Hawlucha

Edit (9.8.2016): Added Corocoro reveals.

Edit (10.8.2016): Added Namakobushi.

Edit (11.08.2016): Added Japanese trailer reveals.

2. Added English trailer reveals.

Edit (18.08.2016): Added Gamescom reveals.

Edit (19.08.2016): Added Worlds reveals. Removed Pyukumuku's second stage, as it seems it is a single stage mon.

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(01.09.2016):
 https://www.youtube.com/watch?v=Rt-4Hef90VA Ditto is shown in the Japanese trailer.

Edit(06.09.2016):
https://www.youtube.com/watch?v=YR1ssSZfoGY

Edit(20.09.2016):
[url]https://www.youtube.com/watch?v=yhNJ7pX12Tw&feature=youtu.be[/url]
Poliwrath, Chansey, Parasect, Scyther, Magmar appears in Japanese trailer.
[url]https://www.youtube.com/watch?v=m8lfI66T5II&feature=youtu.be[/url]
Cloyster appears in English trailer.

Edit 2: Added current reveals. Created a separate Ultra Beasts section.

Edit (04.10.2016):
Japanese trailer showcased Swablu, Shroomish, Seaking and Magneton models.

Icons will be discussed below.

[url]https://www.youtube.com/watch?v=n9o552CaJV8&feature=youtu.be[/url]

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.

[url]https://www.youtube.com/watch?v=ciqAkdXQ9dw[/url]

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.

Edit (14.10.2016):
All the recent updates have been added.