Burger Factory is a fairly new burger joint on Sacramento between Drumm and Davis (next to the new Focaccia Market, in the old Focaccia space, and owned by the same people). Early on, they were having a little trouble getting the burgers right consistently, but I was in there today and it looks like they've got it down.
These aren't hand-formed "gourmet" burgers. But they are made with Golden Gate natural Angus beef (see below) and served on their housemade ciabatta or whole wheat buns. I'd say they're in the same niche as Bistro Burger, but better, and here's the thing: cheaper. A double cheeseburger set me back $3.95. You can add fries (fresh cut in house) and a drink from another $2.00.
Good burgers, great prices!
Also, I'd like to give kudos to the owners of Focaccia Cafe and Bakery and Burger Factory. When I worked around the corner and they were our catered lunch regular I took them for granted, but now that I work a few blocks away I realize how lucky I had it. They're putting out a consistently good product, using good ingredients, at the same prices as other places that aren't half as good.
By far the best price/quality ratio of any lunch place I know of in the FiDi.