Some things you might like to consider before you decide what to plant.....
Available space- You don't want to plant something that will soon out grow your borders.
Is it usually waterlogged, year-round or just a temporary thing with all the recent rain ?
Soil type- Acid or alkaline ?
I will assume for now that the soil is fairly moist, most of the time and you don't have that much space and it's also on the acidic side...
A compact blueberry may do well and will provide delicious fruit!
The one I recommend is Vaccinium corybosum 'Sunshine blue
the leaves are blue-green, flowers pink-white followed by big purple berries
Or perhaps a close relative the evergreen huckleberry- Vaccinium ovatum (box huckleberry) small shiny dark green leaves, pink flowers followed by small black berries
Both shrubs prefer acidic soil, so add plenty of ericacious compost at planting time