Trading with non-player characters makes a return in Gold and Silver, this time with more obvious advantages. Only one Pokemon in the game is only gotten via trading this time around, and you won't encounter it until Kanto. Some of the trades offer rare Pokemon for common Pokemon, and some offer rare Pokemon for rare Pokemon. It's up to you whether you want to make the trades or not though so choose wisely.

Violet City: Onix

Location: Violet City

Method:
The first trade you are offered is made in a home in Violet City. This trade offers you a strong Onix in exchange for the rather common Bellsprout, which can be found outside of Violet City in the grass. Onix is great for the first and second gyms and will prove useful in the fourth, seventh, and eighth after it evolves into the Steel-type Steelix. Definitely a great alternative to Geodude.

ROCKY ♂
Level ??
OT:KYLE
ID:48926
Hold Item:
Bitter Berry
  
  
Trader requests a Bellsprout
Goldenrod City: Machop

Location: Goldenrod City

Method:
A trainer offers you their female Machop in exchange for Drowzee inside the Goldenrod City Department Store. Drowzee can be caught on the route south of Goldenrod City, whereas Machop can't be found until you reach Mt. Mortar. Machop is very handy against Whitney's Miltank, Jasmine's Steelix, and Pryce's Piloswine, so consider this trade.

MUSCLE ♀
Level ??
OT:MIKE
ID:37460
Hold Item:
Gold Berry
  
  
Trader requests a Drowzee
Olivine City: Voltorb

Location: Olivine City

Method:
This trade is a bit useless. Magnemite can do everything Voltorb can and has Steel-typing for added protection, and is caught near Ecruteak City anyways. If you really want to use Electrode, wait until you reach the Team Rocket Headquarters and can catch a Level 30 one.

VOLTY
Level ??
OT:TIM
ID:29189
Hold Item:
PrzCureBerry
  
  
Trader requests a Krabby
Blackthorn City: Rhydon

Location: Blackthorn City

Method:
Rhydon can be hard to get, but Dragonair even more so. Not only that, but yours has to be female. It's not really worth it considering Dragonair will be more help against Clair than Rhydon will be.

DON ♂
Level ??
OT:EMY
ID:00283
Hold Item:
Bitter Berry
  
  
Trader requests a female Dragonair
Pewter City: Rapidash

Location: Pewter City

Method:
You can get Rapidash on Mt. Silver's plains. Plus, Gloom is more helpful against Brock and Misty than Rapidash will be. It's not really worth it.

RUNNY ♂
Level ??
OT:CHRIS
ID:15616
Hold Item:
Burnt Berry
  
  
Trader requests a Gloom
Route 14: Aerodactyl

Location: Route 14

Method:
The only Pokemon exclusive to trades in these games is Aerodactyl. However, you'll need to trade the elusive Chansey to get it. It's a decent trade off unless you like Chansey, and Aerodactyl can provide some great late game support, ripping through Erika and Blaine's teams without a problem.

AEROY ♂
Level ??
OT:KIM
ID:26491
Hold Item:
Gold Berry
  
  
Trader requests a Chansey