We've also got this, which is close to 5 feet tall now and has not (and does not look like it's close to) flowered. I have been keeping it, waiting to see what it is, but we have it in several places, and it's certainly growing like a weed.

1.Sonchus

Thank you, saltcedar,

I have already started pulling this. For such a big, imposing looking weed, it's almost amusing how small the root system is. This is my new favorite weed!