How Does Your Garden Grow?

For the first time since I was a kid with a patch of flower bed behind the shed, I'm attempting to grow food. As you can see, I'm starting small this year. My "garden" consists of five potted plants on my second-story balcony. Allow me to introduce you:

Top left: two mini bell pepper plants (I'm hoping to roast a lot of peppers later in the season)

Top right: basil (pesto here I come!)

Bottom left: cherry Roma tomato plant (I'm afraid it won't get enough sun here - I might have to take it to work with me)

Bottom right: mystery plant... I got the planter from a friend and just let it be, soil intact. This thing sprouted several weeks ago and is growing... well, like a weed. Which it might be. Anybody recognize it?