Previously set for an April 12 introduction, the Zune HD 64, boasting 64GB of internal storage space, has started selling via the Zune Store, obviously, only in the US. The new model can be loaded with up to 16,000 songs or 20 hours of HD video, and features the same specs as the 16GB and 32GB versions - 3.3-inch (480x272) OLED screen, built-in FM radio receiver, 802.11b/g WiFi, and an Nvidia Tegra SoC to power everything.
The 64GB Zune HD costs $349.99 and apparently doesn't include the v4.5 fimware rolled out earlier this week. Luckily, the upgrade is just a download away
Source: TechConnect Magazine - Microsoft Zune HD 64GB debuts early