What is this weed and how do I get rid of it?

[MeredithMan]

This invasive weed began in a planting bed of lillies and has now spread to the surrounding lawn area over the last couple years. It just mocked me and laughed at me when I put down the Scotts Turf Builder plus Weed Killer. Any thoughts as to what this thing is and how to get rid of it? (I did pull it out of the planting bed the old fashioned way a couple years ago, but the darn thing came back)

Thanks!