Can old Corollas be had for $1k yet? If so, that might be a decent option that meets your "meat behind the driver's seat" requirement.
Otherwise, I think you'd do well to go after the SL1 Saturn. They're capable of returning good economy with a motivated driver.
And if you're not interested in the Geo hatch because of the lack of rear crumple space, and are handy (I s'pect so), what about dropping a 1.0L into the usually 1.3L Metro/Swift sedan? See this car:
54.2 after lowering car, 4 mpg gain
(Thread is about lowering, but look at his garage entry - it's a 1.0L conversion.)
Last but not least, you're right: a dedicated thread/article that lists options for cheap, efficient used cars is a great idea.