So you've read our exhaustive review of the NVIDIA SHIELD and decided that it's the Android TV device for you. Whelp, it's available for purchase right now in the US, from both NVIDIA's own store and Amazon.com. The standard 16GB SHIELD is $199.99, but it looks like the SHIELD Pro ($299.99) with its 500GB internal hard drive won't be available until June. According to the NVIDIA Store it's coming on the 3rd, while Amazon says it won't be in stock till the 12th.
SHIELD comes with $30 of free Google Play Store credit and 90 days of Google Play Music All Access. If you buy the more expensive model, you'll get the Android version of Borderlands: The Pre-Sequel for free when it launches in July.
The various SHIELD accessories are also available. Extra controllers are $59.99 (though the SHIELD also works with generic Bluetooth controllers, USB mice and keyboards, or even USB versions of the Xbox 360 controller). The swanky SHIELD Remote, which includes a microphone for voice commands and a headphone jack for private listening, is $49.99. The SHIELD's vertical stand, which reminds me a lot of the PS2 stand from way back in 2000, is $29.99. Amazon is delayed by about three weeks on the stand.
For some reason Best Buy seems to be lagging behind - their listing shows the SHIELD as "coming soon," and doesn't even have a photo of the unit. NVIDIA's store charges shipping, but Amazon should offer free economy shipping or free two-day shipping if you're a Prime member.