Lots, but gravel + boggy ground don't go together very well: gravel is all about hot dry gardens and plants that like to keep their necks dry.
the other watchout for boggy ground is that plants that like it are often attractive to slugs (who like boggy ground because it is moist and slimy for them).
However, boggy stuff can be fantastically dramatic because wet shade is good for plants that grow huge and fast and dramatic. also depends how boggy really, lots of very ordinary stuff will grow if it's not too dark and soggy - like cranesbills, ladies mantle
So top of head, hostas, hydrangeas, rheums (fleshy rhubarby things), thalictrum, some of the sedgy-grasses, the tall white tobacco plant nicotiana sylvestris, bog salvia (very tall wispy blue pretty), angelica, marbled arum, acanthus (bears breeches). if it's not hopelessly soggy but just shady and not dry then japanese maples. some roses don't mind shady - check the david austin catalogue or website. Siberian irises (blue/spring) but not the summer bearded ones. Heuchera, tierella, - ooh you've really got me started now!