Indian Pink (Spigelia marilandica) doesn't get going here until the dicentra are just about finished, and they seem to like the same conditions.
Do toad lilies like to be kept continuously moist? I don't have any planted yet, but I was thinking that they do. Can dicentra take those conditions, or do they prefer to dry a bit over the summer? My dicentra and Indian Pink are all in *you're on your own* areas that don't get watered, but the idea of toad lilies and dicentra growing together is intriguing.