That is a tomato plant. We've always said that because it is in the deadly nightshade family it is toxic, however just yesterday or the day before there was a nice thread about this and the consensus was that it really isn't toxic. I'll try to find the link to that thread for you.
Oh my gosh!!! Too funny! I've been looking at them thinking they were tomatoes but I thought I was crazy because I didn't plant tomatoes this year! I had nice grape tomatoes planted last year but didn't replant them and I ripped this bed apart when we turned it into his habitat LOL! I dug it all out and replaced the soil. I can't believe that somehow the tomatoes came back. I didn't even think it was possible for tomatoes to come back year after year! I'm so mad, before I posted I ripped out two of the plants because I didn't know what they were!