Mint needs a lot of sun, too. I have mine growing in the bog filter. But before I had the pond, I had mint, and it positively went WILD. Grew all over the yard, even inbetween cracks and out onto the driveway. Even with little watering - go figure... I'm thinking there must have been a leak somewhere, feeding it water.
Popular around here are these floating "islands" of cork bark, about a foot square, with holes drilled in them to accommodate plastic flower pots. You stick your plants in, and they develop water roots, and float around in your pond. Really cool. Just about any type plant will work, surprisingly. And the pond store has tons of them made of succulents. In fact, those succulets are what they recommend most, for the floating island gardens. Somehow, when they're put in water, they develop the type of roots to adapt to a wet, rather than arid, environment.