Miscanthus do fine in marshy soils in full sun. Panicum is fine as well though there is some potential for self sowing on moist open ground. Juncus love the conditions you mention. What is native to those conditions in your area?? Natives look so good and make so much sense!

Panciums for me are my best full sun and wet soil tolerants. I have done a entire bottom side of a hill with Panicum v. "Dallas Blues". The intensity of the purple blooms with the powder blue foliage comes in handy for that striking combo with perennials and shrubs. P.v. "Heavy Metal", and P.v. "Cloud Nine" prove to me and my trial gardens that they can stand wet feet, as well as the heat that comes around year at this time of the year. Miscnathus "Rotsilber" is really nice for the colors and sturdy root system. Molina caerula and its cousins are great for boggy and moor like conditions. Many varieties include "Heidebraut", "Moorhexe", and "Strahlenquelle" to name a few...

The Molinia species are among the most pleasure-giving of grasses, and those mentioned are my favorites. They do like moist to wet soil and full sun (no standing water, though).

Many other grasses do well in moist soil (as long as the drainage is good): most of the Miscanthus, Calamagrostis x a. 'Karl Foerster' come quickly to mind. Be mindful, though, that Miscanthus will probably throw seed in those conditions in zone 8 and that not ALL Carex like wet conditions.