It's the bottom left one with the title "Sponsor Links"
Picture of it (marked with a blue box) here:

I had Adblock Plus and NoScript temporarily disabled to take this screenshot. I have gotten rid of all the other ads and the whole left column, save for the "Sponsor Links" one. But because I cant get rid of that one, the left column still hogs like 250 pixels in width, which really sucks when you only have a 1024x768 pixel resolution. I really need to get rid of that one, if possible. I am all out of ideas now, having spent the last 4 hours trying to figure it out. Maybe I'm just dense, but all I know is I'm stuck.
I know there's a "Remove column" link, but that only leads to a subscription signup page to become a paying member. Not an option for me.
Thanks in advance for any and all help I can get. God knows I need it.
//SP