Here's my 20G paludarium. Fire Belly Toads up on the land, cardinal tetras and dwarf cories in the water along with a few shrimp. The land is way more covered in plants now...a few aquatic mosses, a dwarf anubias and a small crypt that's grown out of control. In the water is whatever I can get to grow in my low-tech conditions. In the far back corner is a waterfall with a "water column" behind it...the canister output is in there, where it goes through a UV, and then passes by the heater, keeping them out of the tank. The second picture shows that (though I have a bigger canister now). The filter intake is PVC built into the construction with a large sponge on one side. The waterfall goes into a little pond (which has a little fogger in it on a timer, with a craft mesh cage so the frogs don't get hurt by it), which then flows down a little river along the front of the glass into the tank.
Construction was with thin plexiglas (for the water column), great stuff foam, and a LOT of black 100% silicone. Oh and some green craft mesh to cover anywhere the frogs may escape, including the area between the top of the waterfall and the glass. There's shale that lines the bottom of the pond and river, along with little chunks to form outcroppings in the waterfall. There's also two larger pieces siliconed in 2 of the corners, one above the pond/river to give more land area and plenty of shade underneath, and one just barely in the water in the tank.
It's on a counter between the living area and the kitchen, so designing it with as many viewing angles as possible was highly important. I'm really happy with how it's turned out, I only wish I had room for a bigger one. It's been going for over a year now with very few issues.