breeding water turtles is hard in an aquarium, and you will need a lot of filtration et etc
----so no turtles
if you ever see an adult Tiger salamnder spending any real time in the water something is wrong! they are terrestrial species that are aquatic in their larval stage, during breeding and hibernation, and maybe the occasional 'dip'
----so no tiger salamanders
as far what you aare looking for--nothing comes to mind. (assuming that you envision your critter spend a good deal of time on land and in the water-and doing more than what could be accomplished with a simple water dish or a floating log).
--why not try for something easy and local---some easterm newts for the water part- they will eat little guppies and little shrimps, and maybe a toad or local frog that will sit on the land most of the time(of course you will need to feed the land critter some crickets)