for amphibs, i would go with something like a salamandar or a newt. newts are a lot of fun.
If the tank is relatively tall, you could even try a tree frog, but go with something somewhat hardy, like a green tree frog. No red eyes or white lips.
maybe a vietnamese moss toad
you might even be able to do a water snake, if you get a pygmy. but it too will eat the fish.
if you have at least 30% land, you could do anoles or certain small geckos.
just make sure whatever amphib or lizard you get, you really watch it for a while and get it hooked on bugs, not fish. and try to set it up so that the amphib/lizards are smaller than the fish, or are definately not going to be able to swallow it whole.
i am also thinking about a water terra. i want to set one up, but really can't think of any amphibs/lizards that won't eat a fish if the fish is small enough.