The 2nd CTP for Parallel Extensions to the .NET Framework 3.5 was released recently.
Download the Parallel Extensions June 2008 CTP
Parallel Extensions simplifies development by providing library-based support for introducing concurrency into applications written with any .NET language, including C# and Visual Basic. It includes the Task Parallel Library (TPL), which provides imperative data and task parallelism; Parallel LINQ (PLINQ), which provides declarative data parallelism; and all new Coordination Data Structures (CDS), which provide support for work coordination and managing shared state.
In addition to CDS, this upgrade provides several improvements, including a new scheduler that is more robust, efficient, and scalable. TPL also exposes new functionality, including methods for continuations. PLINQ now runs on top of TPL, clarifies order-preservation, and provides several new operators.
This download works with the .NET Framework 3.5 as a simple, small-footprint installation that drops a single DLL, documentation, samples, and registers the DLL with Visual Studio 2008.