Dart frogs have very specific needs. Before you get any you must have temperature and humidity under control. You also need to have a steady food supply of fruit flies established. None of this is particularly difficult but needs to be in place. The species that Kurt mentioned are great beginner darts if the conditions are correct. 4 in a 75g is fantastic. You will want a glass top.

Here is a little reading to get you started.
http://www.frogforum.net/food-feeder...html#post17640

This article is great for all darts as far as habitat and environmental conditions go.
http://www.frogforum.net/dart-frog-m...-breeding.html

Any questions feel free to ask.