A few options. Outside of GH, you can try Mobsters and Seals on Kokomo Beach. They seemed to do alot better for me, once I hit the higher levels. Also the Alarms in the clocktower. They're on the third floor, I believe. They're worth a little more than the seals are, but they don't spawn as close together as the Seals do. So you end up wandering a little bit more.
Mobsters are a nice bonus, because you can steal Saphires from em. Get yourself a little bit of cash while you're leveling. A warming with the Seals, though. They have some sort of spell that can kill you in pretty much one hit, if you're not careful.
You can also try mobbing in Gh. Hide and GT them. =\
Depends on how froggy you're feeling, I suppose.