I've had the Razr for a week or so. As with any gadget, I bought a bunch of accessories as soon as I got the phone. Here are my impressions of a few of them:
The Otterbox Defender case and holster from Verizon: This case really makes me feel that my phone is safe. It is extremely well-designed. The Hard shell fits snugly around the phone and the silicon gives nice shock protection and good grip. The silicone actually makes the side buttons easier to press and use and the covers for the ports is a nice touch. It includes a very tough built-in screen protector and has a nice raised lip around the screen, so the screen is very well-protected. The holster holds the phone well and the belt-clip doubles as a kickstand.
The drawback is that this case makes the phone a lot larger and heavier. It nearly doubles the weight of the phone. The slimness and light weight of the phone are its greatest assets, so it is kind of sad covering them up. Also, the screen protector is a glare-reduction model, so it distorts the image slightly. It isn't unbearable, but gives the screen a sparkly appearance. The holster's kickstand is rather unstable, and taking the phone out of the holster is more awkward than necessary.
Even so, if you want your phone to be safe, this is a great way to go.
Motorola Droid RAZR XT912 Shell Holster Combo W/ Kick-Stand from Amazon: This case fits the phone very snugly and doesn't add much size or weight. The kick-stand is pretty handy and reasonably stable. The material is a hard plastic, and is textured for good grip. It does provide a slight lip around the screen to give a little protection. The holster seems to hold the phone securely and it is fairly easy to insert and remove the phone.
Unfortunately the case offers no protection to the phone's top ports. The case makes pressing the power button a little difficult due to a raised lip around the hole for the button. Even with the texture, the plastic is a little slick, which is good for sliding it in a pocket, but not good for laying it on a dashboard.
This is a much more slim option and seems to offer a reasonable amount of protection.
Diztronic Matte Back Black Flexible TPU Case for Motorola Droid Razr (Verizon & Rogers) [Diztronic Retail Packaging] from Amazon: This was a very inexpensive silicone type option. The case is lightweight and adds very little size to the phone. The texture is nice, not too sticky but adds a little grip.
The protection offered by this case is limited. It will protect the phone's finish, but probably won't protect against too much more.
If I try others, I'll review them, but I thought people might want a little more information to help decide which case to get.