Nexus S is the dream phone for Android users -- it's called the pure Google experience where you are free to do what ever you want. We bought the phone for some $529+, but Best Buy is offering this phone for free of cost. On 3rd August you can get this phone for for $0 from any Best Buy store.
The catch -- you will have to get a 2 year contract with any GSM network including AT&T, T-Mobile and Sprint. The contract-less cost of the phone is $529 on Best Buy.