Another theme I've seen but never tried, is the half land half water set-up, looks seriously cool; means you could possibly house small shoals of fish, with reptiles that occupy the land part
I think you might be talking about a paludarium, definitely a neat idea, and if planned correctly can be a lot of joy to run and maintain especially if you can find animals to occupy both the land and water protions of the tank...
If OP wants to keep it as just either water or land though, then i would possibly recommend a puffer for a fishtank...