Target also has the 16GB models at $479. So if you have no Walmart near you but have a Target, you can try to price match to them.
I can confirm it is ONLY the 16GB models with the $20 price reduction at Target. I stopped by at 8:30 this morning on my way to work and got a 32GB white/silver model, rang up $599. Guy in electronics scanned the 16GB and it came up $479, 64GB $699. So only the 16GB is on sale. Got my 5% off with Red Card too. I was in an out in under 5 minutes.