This guy has been growing like gang busters in a newly planted bed of ground covering sedums. It's actually kind of a nice ground cover but based on its rate of spread and the fact that I didn't plant it I'm thinking of yanking it all up.
It has oblong, almost jade-like leaves; grows from a ground hugging stem that sprouts radially from a rooted base. No flowers yet, but it spreads aggressively both in the garden and pavement cracks. Seems to prefer dry areas.