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I would recommend the invisible shield. If you truly want to protect your ipod, this will be the best. If anything, get the invisible shield (full front and back) and then put another case over it if you want one.

Edit: what part of SD are you from?
 
Check out the amazing in-depth reviews on iLounge for the best information.

But, basically:

InvisibleShield/other protective film:
Pros: Good scratch protection, no added size or weight.
Cons: No impact protection

Skins/rubber cases:
Pros: Good scratch protection, good impact protection.
Cons: Adds size and weight, attracts dust.

Soft cases:
Pros: Good scratch protection, ok impact protection
Cons: Adds size and weight.

Plastic Hard Cases:
Pros: Good scratch protection, ok impact protection,
Cons: Adds size and weight, easily scratched.

Metal Hard Cases:
Pros: Good scratch protection, Good impact protection.
Cons: Adds a lot of size and weight.
 
I have a Protech on my iPod. It's the only thing I'll use. I also have one on my SLVR and my PSP, and my wife has one on her RAZR phone and 1st Gen. Nano. It's the same thing as the InvisibleShield, but a little less expensive. My wife's kind of hard on her phone, and it's held up pretty well. You can find them at www.protechyourdevice.com

J.
 
I would recommend the invisible shield. If you truly want to protect your ipod, this will be the best. If anything, get the invisible shield (full front and back) and then put another case over it if you want one.

Edit: what part of SD are you from?

I agree with the invisible shield. I prefer to see the beauty of my iPod as Apple intended, and this protects it from the everyday wear and tear.
 
I have the iSkin evo3, I think it's called. I love it, protects my iPod from falls, scratches, has some water protection, sand, dust etc:)
 
For uber-protection I'd go for a Power Support Crystal Film set and a Contour Showcase. A brilliant little combo...
 
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