We all knew it was coming, and now here it is.
Dell.com is now selling the Streak unlocked in the US. The price? The very same $549.99 that the AT&T-locked device sells for when purchased without a contract. [see update below]
The official specs haven't been updated so it isn't clear whether this unlocked version will be able to hop onto T-Mobile's 3G network. My gut feeling is no, but it looks like we won't know for sure until after December 7th, which is when this new breed of Streaks is expected to ship. Which OS will be preloaded isn't explicitly stated on the site either, but considering that units purchased at Best Buy are supposed to get updated to Froyo on the 3rd and "later in December" is the ETA of when other carrier-locked Streaks will get it too, it seems like a pretty safe bet that these unlocked devices will be running Android 2.2 out of the box.
Of course, if you don't want to wait until next month, there are already several ways to unlock the AT&T Streak for use with T-Mobile (phone and EDGE only), as well as a few methods to get (unofficial and official) Froyo up and running before Dell serves it to you.
[Dell] Thanks, chike99!
UPDATE 11/23: The unlocked 16GB Streak is now listed at $579.99. Other options (Froyo, 32GB, and New Cherry Red) are also available. See this post for more details.