If you're looking to strike the perfect balance between full-phone protection and still maintaining a slim phone, the Trident Cyclops Series Cases for HTC EVO 4G are the way to go. You're still getting all of the dust and particle-covering rubber that you get from some other offerings (like the Seidio CONVERT Combo) but without the same bulk and heft that mandates it goes on a belt holster.
The Trident Cyclops Series actually comes in two parts: the hard, plastic shell that surrounds your phone, and the rubberized skin that goes around the outside edges of the shell. The rubber feels fine in hand, and that's where you're actually getting all of your dust rejection powers. The rubber skin covers all of the open ports on the phone as well as volume rocker and power button, ensuring nothing gets in.
One of the cooler features of this case is that it comes with a built-in screen protector, not unlike the Otterbox Defender line of cases. When the phone is in the case, you can't even tell there's a thin plastic screen separating you from your phone's screen, but if you're anal like me, you'll be spending a lot of time trying to make sure there's no dust on the phone and the screen protector before finally locking your EVO inside.
Best part? You don't lose access to your kickstand! That might sound silly, but I use my kickstand often, so getting to keep my phone massively protecting and getting to flip out my kickstand at a moment's notice is too sweet a deal for me. You can pick up the Trident Cyclops Series Cases for HTC EVO 4G in the Android Central Store for $32.95.