The New Ringke by Rearth is one of the better Silicone cases I've come across for the iPhone 4. It retails for $16.99 on their website and its available in a plethora of colors. Its a really slim case and the case is shaped exactly like the iPhone 4 itself, it goes as far as to putting the notches of where the antenna is on the device.
Looking around the case you'll find that the buttons are covered up, the bottom has three separate cutouts for the speaker, mic, and 30-Pin connector, and up top you have an ample cutout for the headset jack and second mic.
The case feels like a blend of TPU and Silicone material. Its pretty flexible, but it has a sandy feel overall and slips in and out of pockets without a problem. The Camera cutout is nice and big, so no issues with the LED flash. it also has a cutout for the apple logo, but unlike most cases where its just an open circle, they've actually outlined the Apple Logo itself and it provides for a very sharp look. The Case also has a nice lip that goes over the glass to provide a lay on table design. The rubber on the sides goes up right to the glass and you get great bezel protection.
However, there are a couple problems. The sides are extreme flimsy and loose. Also the bottom lip will start to sag over time. Other than that it's pretty good
The logo on the case is on the back (see picture above) but it's nice and subtle. Overall I really recommend this case, you will not be disappointed. It provides great all around protection while having a nice slim design. It fights nice and tight over the phone and you really won't find case quite like it.
Overall, they're really nice cases. However, because of the loose fit, it really isn't for everyone