All over the place. There's Slowpoke in Slowpoke well, and I believe you can surf and find Poliwags in certain small water patches. Psyducks and Golducks are also found in the surf water above Goldenrod city.
As for non Water type surfers, there are Tauros (great pokemon but poor Special Attack stat for surfing), Miltank, Furret, and Nidoking/Queen.
I also really don't mind Tentacool and Tentacruel. Fantastic special defense, Surf provides a good damaging attack, and Toxic Spikes is also great.
Currently Playing: Skies of Arcadia, Heart Gold, Fire Emblem, Reverse of Arcadia Reading: Sgt. Fury and his Howling Commandoes, The Unwritten, Starman.
I wish they'd make SPLASH able to do damage, like one in a thousand times, and have it be like a OHKO move that wipes out the entire party of the other team...lol..like it creates a giant wave of water somehow that creates a tsunami, and just destroys everything...that way I could actually keep my shiny magikarp on the team and not use it as a not so rare red gyrados..