Picked mine up at blockbuster for 5 bucks.
Works great for non stylus games as the ergo friendly shape eliminates those ds hand cramps. Gives you like 6 hours more playtime when it's fully charged too.
Only thing I don't like is that it stretches out the stylus slot a bit and makes it very easy for the stylus to slide out of it's holster when the ds is not in the grip.