GSI Outdoors Glacier Stainless Steel Bottle Cup
Price Paid: $9
This is actually two reviews. Why? Because for some weird reason, GSI was originally producing this in a size that in a diameter that would fit around the bottle of a standard 1L Nalgene. Then they decided to make it slightly smaller, just slightly; now, it won't stack with a Nalgene bottle. Who knows why; it certainly makes zero sense.
If you find one that will fit around the bottom of your Nalgene, 4.5 stars -- perfectly fine steel cup, good handholders, and a nice space saver.
If you find out the current model, 3 stars. Fine steel cup, but now it is taking up more space in your pack.