
Starter is first Pokemon in all games except Yellow:

Oddish (Route 24)

Charmander (Route 24)

Magikarp (Route 4 Pokemon Center)
R/B/Y/FR/LG - Rattata (Route 1)
G/S/C/HG/SS - Sentret (Route 29)
R/S/E - Zigzagoon (Route 101)
D/P/Pt - Bidoof (Route 201)
B/W - Lillipup (Route 1)
B2/W2 - Patrat (Route 19)
X/Y - Bunnelby (Route 2)

R/B/FR/LG - Pikachu (Viridian Forest)
Y - Pikachu (Starter)
G/S/HG/SS - Mareep (Route 32)
C - Pichu (Odd Egg from Day Care Man)
R/S/E - Electrike (Route 110)
D/P/Pt - Shinx (Route 202
B/W - Blitzle (Route 3)
B2/W2 - Mareep (Floccesy Ranch)
X/Y - Pikachu (Santalune Forest)

R/B/Y/FR/LG - None before 3rd gym
G/S - None before 3rd gym
C - Smoochum (Odd Egg from Day Care Man)
HG/SS - Smoochum (Dim Cave Pokewalker Route*)
R/S/E - None before 3rd gym
D/P - None before 3rd gym
Pt - Eevee (Hearthome City from Bebe)
B/W/B2/W2 - Swinub (Icy Cave DW Area*)
X/Y - Amaura (Fossil revival)

R - Mankey (Route 5)
B - None before 3rd gym
Y/FR/LG - Mankey (Route 22)
G/S/HG/SS - Poliwag (Violet City with Old Rod)
C - Poliwag (Route 30)
R/S/E - Torchic (Starter)
D/P/Pt - Chimchar (Starter)
B/W/B2/W2 - Tepig (Starter)
X/Y - Chespin (Starter)

R/B/FR/LG - Charmander (Starter)
Y - Pidgey (Route 1)
G/S/C/HG/SS - Hoothoot (Route 29)
R/S/E - Wingull (Route 103)
D/P/Pt - Starly (Route 201)
B/W - Pidove (Route 3)
B2/W2 - Pidove (Route 20)
X/Y - Fletchling (Route 2)

R - Weedle (Route 2)
B - Caterpie (Route 2)
Y - Caterpie (Viridian Forest)
FR/LG - Weedle (Route 2)
G/HG - Spinarak (Route 30)
S/SS - Ledyba (Route 30)
C - Caterpie (Route 30)
R/S/E - Wurmple (Route 101)
D/P - Kricketot (Route 202)
Pt - Kricketot (Route 201)
B/W - Sewaddle (Pinwheel Forest)
B2/W2 - Sewaddle (Route 20)
X/Y - Scatterbug (Route 2)

R/B/FR/LG - Bulbasaur (Starter)
Y - Nidoran (Route 22)
G/HG - Spinarak (Route 30)
S/C/SS - Weedle (Route 30)
R/S/E - Wurmple (Route 101)
D/P/Pt - Budew (Route 204)
B/W - Venipede (Pinwheel Forest)
B2/W2 - Venipede (Route 20)
X/Y - Weedle (Route 2)

R/B/Y - Nidoran (Route 22)
FR/LG - Nidoran (Route 3)
G/S/HG/SS - Geodude (Route 46)
C - Phanpy (Route 46)
R/S/E - Mudkip (Starter)
D/P/Pt - Turtwig (Starter)
B/W - Drilbur (Wellspring Cave)
B2/W2 - Sandile (Route 3)
X/Y - Bunnelby (Route 2)

R/B/Y/FR/LG - Geodude (Mt. Moon)
G/S/C/HG/SS - Geodude (Route 46)
R/S/E - Aron (Granite Cave)
D/P/Pt - Geodude (Oreburgh Gate)
B/W - Roggenrola (Wellspring Cave)
B2/W2 - Roggenrola (Relic Passage)
X/Y - Rhyhorn (Glittering Cave)

G/S/C/HG/SS - Onix (Union Cave)
R/S/E - Aron (Granite Cave)
D/P/Pt - Piplup (Starter)
B/W - Drilbur (Wellspring Cave)
B2/W2 - Riolu (Floccesy Ranch)
X/Y - Burmy (Route 3)

R/B/Y/FR/LG - Abra (Route 24)
G/S/C/HG/SS - Slowpoke (Slowpoke Well)
R/S/E - Ralts (Route 102)
D/P/Pt - Abra (Route 203)
B/W - Munna (Dream Yard)
B2/W2 - Woobat (Relic Passage)
X/Y - Fennekin (Starter)

G/S/C - None before 3rd gym
HG/SS - Murkrow (Suburban Area Pokewalker Route*)
R/S/E - Poochyena (Route 101)
D - Murkrow (Eterna Forest)
P - None before 3rd gym
Pt - Eevee (Hearthome City from Bebe)
B/W - Purrloin (Route 2)
B2/W2 - Purrloin (Route 20)
X/Y - Froakie (Starter)

R/B/Y/FR/LG - None before 3rd gym
G/S/C/HG/SS - Gastly (Sprout Tower)
R/S/E - Nincada (Route 116)
D/P/Pt - Drifloon (Valley Windworks on Friday)
B/W - Misdreavus (Spooky Manor DW area*)
B2/W2 - Drifloon (Dream Radar*)
X/Y - Honedge (Route 6)

R/B/Y/FR/LG - None before 3rd gym
G/S/HG/SS - Dratini (Goldenrod Game Corner)
C - None before 3rd gym
R/S/E - None before 3rd gym
D/P - None before 3rd gym
Pt - Gible (Wayward Cave)
B/W - Trapinch (Rugged Mountain DW area*)
B2/W2 - Swablu (Dream Radar*)
X/Y - Axew (Connecting Cave)

X/Y - Azurill (Route 3)