According to the official Windows Vista Team blog, the first developer beta of Service Pack 2 for Windows Vista will be released on Wednesday 29th October.

The blog states that SP2 adds the following features to Vista:

• Windows Vista SP2 adds Windows Search 4.0 for faster and improved relevancy in searches.
• Windows Vista SP2 contains the Bluetooth 2.1 Feature Pack supporting the most recent specification for Bluetooth Technology.
• Ability to record data on to Blu-Ray media natively in Windows Vista.
• Adds Windows Connect Now (WCN) to simplify Wi-Fi Configuration.
• Windows Vista SP2 enables the exFAT file system to support UTC timestamps, which allows correct file synchronization across time zones. 

There's no indication when the final release of SP2 will be.