A starter frog... hmmm... I would go with some of these...
1. Bait Shop Frogs :P Mostly because you save lives, and you can make some really nice vivariums for them.
2. American Toads
Get them as tads from the wild. Its a lot of fun raising them from tads and seeing how fast a small toad can become a massive, man eating giant :P Activity level at my house with these fellas is quite high
3. Green Tree Frogs, they are green, cool looking and stick to glass. Hardy animals as well
4. Firebelly Toads , Mucho Hardy and amazingly active species. Fun to watch. Careful, these are escape artists for sure!!!!
5. Whites Tree Frog
Awesome frogs, great personalities, not THAT hardy and sleep during the day like Green Tree Frogs.
Please not that the majority of these frogs are indeed nocturnal. The only diurnal species are the Poison Dart Frogs, but I do NOT recommend these as starter amphibians.
Just my 50 cents :P