I did some research, and I found a great website that gives information on wildflowers.
These are called Spring Beauty. The name seems particularly appropriate to me. They grow in moist woods and bloom from March to May. They're about 6-12 inches tall.
This is a cut-leaved toothwort. They like to grow in rich moist woods and reach about 8-15 inches. They bloom from April to May. I had never really noticed these before but they are so pretty!
I knew these were violets, but they are called common blue violets. I've seen them in white before (and those are actually my favorites) but they also come in YELLOW! I've never seen those, but they are on my must-see list.