Route 5
Description Of Route 5:
After you have defeated the Cerulean Gym, visited Bill, and have shopped Team Rocket, next only accessible route is to the south of the city. Route 5 doesn't have much in it outside a few Wild Pokemon and the Pokemon Daycare, and since you yet don't have access to Saffron City, you have to take the Underground Path to Route 6.
The only significant thing on this Route / Underground is the next Pokemon Trade. This person can be found right as you enter the building on the underground path, and they'd like a Cubone for their Machoke. The Machoke will evolve into Machamp immediately after the trade, so do this trade as soon as you have a Cubone.
Pokemon In Route 5:
Grasses:
Pidgey - Levels 15-17 - 45% Appearance Rate
Rattata - Levels 14-16 - 25% Appearance Rate
Abra - Level 7 - 15% Appearance Rate
Jigglypuff - Level 3-7 - 10% Appearance Rate
Pidgeotto - Level 17 - 5% Appearance Rate