Pictures and prices for the upcoming Otterbox cases have been posted to their site and look great. Check it out: DROID X by Motorola Cases // OtterBox.com
Not a fan...Otterbox is always way too bulky for me.
...Probably not compatible with the extended battery.
I just ordered Seidio Innocase's & holsters for my wife and I (black and sage) - and will probably get the Rugged addon when it's available as well.
That said - I'm sure I'll also get a Defender once they're released - being the case'whore that I am.
I always liked the Defender on our iPhone 3GS's - but I hated having to put an anti-glare screen protector on to eliminate the oil-slick look from the Defender screen protector. I tried the baby powder trick but it only lasted a while and I can't be bothered to screw around doing that every month or so. Hopefully they got the whole oil slick debacle figured out with the newer Defenders they're making.
If it's not no case will be. (but they all technically are compatible because it's already been noted that the extended battery works with the standard battery door...it's just a little snug.)