Creeping Charlie is the most common ground cover around here. It's also called ground ivy and gill-over-the-ground.
I have had a love/hate relationship with this plant for a long, long time. It grows everywhere. Everywhere. Every. Where.
A lot of people want to get rid of it and if you're one of them, then check out this page for ideas.
In this part of Indiana, where flowers other than iris and daylilies require a lot of soil amendment, mulch and TLC, it's nice to have a filler that works so hard for so little. When people ask what it is, just refer to it by the Latin name, Glechoma hederacea, ("Isn't that Glechoma gorgeous! Just look at how it drapes over that little wall and fills in there!") and they'll think you've put it there on purpose.