DecalGirl.com are the worlds leading supplier of skins for all consoles, they also have a great Ipod section with skins for every version of the Ipod, heres some sampleskins:
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iPod 3G Skins + Wraps

96 in total



iPod 4G Skins + Wraps

99 in total.



iPod Mini Skins + Wraps

119 in total



iPod Nano Skins

166 in total



iPod Shuffle Skins

161 in total



iPod Video (5G) Skins

214 in total