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I got and am still using the white Power Support silicone case. Seems decent enough, though could fit a bit tighter. If I'm holding the phone by the sides and press the sleep button, sometimes it slides around a bit.

It's perfect for what I wanted it for though. Gives a better grip and adds some traction for when I lay it down so it won't try to slide around.
 
i have the power support silicon jacket (off of apples site)

I love it. Was just what i was looking for (protection without sacrificing too much of the shape/adding thickness).

I have not dropped it with it on yet since then. So, not sure how effective it will be but, i have piece of mind. Comes with a couple of the crystal screen protectors as well.

EDIT: I agree with tony^^ it does slide a little. But is not too big of a problem if any at all.
 
I'm a big fan of OtterBox... I have a waterproof case (Armor series) for my 1st gen iPhone, plus ruggedized cases (Defender series) for that 1st gen and 2 more (one white, one pink with proceeds to fight breast cancer) for the 3G I just bought at BestBuy on Saturday.

But they recently introduced smaller rubber/silicon cases (Impact series) like you're probably looking for, for the 3G. I have one of those, too (Full disclosure, I write for iPhone Life magazine, so they gave me a ton of stuff at the Consumer Electronics Show) But despite the freebies, they truly are the most rugged cases out there. Even the new slim case has air pockets on all 4 corners to protect against drops as that's the likely point of impact. Check it out at www.OtterBox.com. I also have a couple of photos up at www.PlanetOtterBox.com (Rock of Gibraltar and Island of Atlantis, Bahamas).

I have Speck cases too (again, full disclosure, they also gave me a bunch of freebies) and they are quite stylish. I've only had my 3G for a couple of days, so I haven't settled on any one yet. But if you are afraid of drops, OtterBox is worth considering.
 
Yesterday I got my Incipio Feather for the 3G. It's terrific. It replaces a cozip case, which is also nice. Neither is silicon, but both add "grippiness" to the phone.

Edit: For the benefit of those who come later, I withdraw this recommendation. The original post was written on March 3. The case failed today (March 20). The strip that protects the chrome above the volume and silence switches broke away. I am not a rough user.
 
incipio
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Agreed, I've been very happy with mine as well; excellent quality.
 
I bought the incase the day I got the phone, 8-31-08. After several months it started "splitting" from the face up to the earphone jack hole. I contacted incase, sending them a photo, and they sent me a free replacement.

When you first get this case, the outside feels kind of smooth and "plasticy" and hard. After a few days it gets a pleasant tackiness that gives you a secure feeling when holding it in your hand.

I really like it and hope the new one doesn't start ripping...had it for 3 months so far...
 
Are there any silicon cases that have a removeable "plug" for the connector dock?
 
toughskin

I have had the Speck Toughskin for both the 2G and 3G, and would have to admit that they are the best by far at protecting either model.
 
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