Some Pokemon will only evole when you trade them...

Machoke = Machamp
Graveler = Golem
Haunter = Gengar
Kadabra = Alakazam
 
 

Or until you give them a stone...

Pikachu + ThunderStone = Raichu
Nidorina + MoonStone = Nidoqueen
Nidorino + MoonStone = Nidoking
Clefairy + MoonStone = Clefable
Vulpix + FireStone = Ninetales
Jigglypuff + MoonStone = Wigglytuff
Gloom + LeafStone = Vileplume
Growlithe + FireStone = Arcanine
Poliwhirl + WaterStone = Poliwarth
Weepinbell + LeafStone = Victreebel
Shellder + WaterStone = Cloyster
Exeggcute + LeafStone = Exegguter
Staryu + WaterStone = Starmie
Eevee + WaterStone = Vapereon
Eevee + ThunderStone = Jolteon
Eevee + FireStone = Flareon