I assume you mean "Evolve via Trading", as your subject says.
This is easily researched on this site as well as others. But I'll answer anyway :)...
Here's the Pokemon that evolve via Trading, by Generation:
Generation I
- Kadabra evolves to Alakazam
- Haunter evolves to Gengar
- Graveler evolves to Golem
- Machoke evolves to Machamp
Generation II
- Poliwhirl evolves to Politoed when holding King's Rock
- Slowpoke evolves to Slowking when holding King's Rock
- Onix evolves to Steelix when holding Metal Coat
- Seadra evolves to Kingdra when holding Dragon Scale
- Scyther evolves to Scizor when holding Metal Coat
- Porygon evolves to Porygon2 when holding Up-Grade
Generation III
- Clamperl evolves to Hauntail when holding DeepSeaTooth
- Clamperl evolves to Gorebyss when holding DeepSeaScale
Generation IV
- Rhydon evolves to Rhyperior when holding Protector
- Electrabuzz evolves to Electrivire when holding Electirizer
- Magmar evolves to Magmortar when holding Magmarizer
- Porygon2 evolves to Porygon-Z when holding Dubious Disc
- Dusclops evolves to Dusknoir when holding Reaper Cloth
Generation V
- Boldore evolves to Gilgalith
- Gurdurr evolves to Conkeldurr
- Feebas evolves to Milotic when holding Prism Scale
- Karrablast evolves to Escavalier, only when traded for Shelmet
- Shelmet evolves to Accelgor, only when traded for Karrablast
Hope that's summary enough for you.