HTC One X International/GSM version - Seidio Surface Case Combo (w/ Holster) $10 or $11 at Amazon

Edit: The one I received was the case only, not the combo, so less of a good deal.

This is a good case for these phones at a much reduced price.

Seidio Surface Case (w/o kickstand) for HTC One X, International/GSM version. NOT for AT&T/LTE version.
Red [amazon.com] - $9.25
Blue [amazon.com] - $10.40

The AT&T/LTE versions are $20+ and up depending on if you want the holster or not.

For the AT&T version, there is a good deal on the Convert Combo for the HTC One X AT&T version [amazon.com], black without kickstand. at $33.94 The Convert Combo provides a second case over the top of the Surface case (included) that takes the level of protection up to approximately Otterbox Defender level.

NOTE: These cases may or may not work with the HTC One X+, Seidio online customer support says they don't, but several places online say they do. Use at your own risk.