Depends on what format you want.
They have an Android right now, and if I wasnt so in love with WP7 I would have picked up the Gzone Commando.
Most of the rest are the basic Casio OS, nothing special. Eventually they might make a WP7 device but I wouldnt bet on it.
Now that smartphones are so popular and you have to pick a platform first, then a device, I'd suggest that rugged phones aren't nearly as important to the market as they used to be.
I'd recommend buying something you like and then finding an Otterbox for it.