in the Route after the Tohjo Falls, before you enter the Pokemon League gate. There's lots of Raticate and Doduo there, as well as some Ponyta and Arbok. Also, there are Tentacool and Tentacruel in the waters that mostly make for a good point count. Of course, I'm building up my Noctowl and Eevee, and they are both at 37 now. But I got Noctowl up 7 levels today just facing the trainers and wild pokemon over there.
There's a house there where a lady will heal your Pokemon, so I just stick around there and go back whenever I need. I want to get everybody up to level 50 before I go on.
Have you visited Alnilam's Realm today?