If you go to backwaterreptiles.com you can see quite a selection of newts and salamanders. I have never bought from them so i'm not sure whether you should order from them, but it would be a good place to start. I would recommend amphiumas as a good species. They are super hardy, awesome looking, will eat pretty much anything that you give them, and can live in an entirely aquatic setup. I have kept fire-bellied newts, but they really don't do much. They are also incredibly stupid. One of the seven that I had killed itself by ramming its nose into the glass. The good thing about them is that they don't need too much space and will eat frozen/thawed blood-worms.
Hope this helps