Are you primarily interested in screen protection, or do you want something to guard against dropping it? techrestore.com has the best price I've found for the Inivisible Shield. That will protect against scratching better than anything else. I use an agent18.com hard case, which probably would protect the iPod once from a fall, but suffer damage itself. So, I carry that in the slipcase that originally came with my Handspring Visor. Nice snug padded fit. Look around ilounge.com for more possibilities.
I'm looking primarily for overall scratch protection, for the screen and body. I've tried clear plastic adhesives before, but I can never seem to get rid of all the air bubbles. That VideoShield cover looks pretty neat though, I might consider it.
I got a skin from www.bestskinsever.com which sells a product just like Invisible Shield for much less. The only difference is that BSE doesn't have the hardcore warranty of replacing anything scratched like IS does. I was wary of bubbles too, but it turns out, if you try applying the skin with Windex, it works perfectly. I'm clumsy, but I still got pretty good results. I have one BSE for my iPod Video and one for my PSP. Works great.