Finish Normal, Start doing Nightmare areas. Andy to Meph should be good from 30 - 50. Then from there, Meph to Baal if you can in Nightmare either as a dual pair, or Terror Zones if you can get past Baal just a single time.
Otherwise find champion packs in Act 3 and 4 and run through them for easy points. Those Kurast dungeon spots are always full of champions and make for easy killing. Arachnid Lair and Spider Cavern are good spots too.
D2:R