1. System.Data.Linq.dll – The implementation for LINQ to SQL.
2. System.Xml.Linq.dll – The implementation for LINQ to XML.
3. System.AddIn.dll, System.AddIn.Contract.dll – New AddIn (plug-in) model.
4. System.Net.dll – Peer to Peer APIs.
5. System.DirectoryServices.AccountManagement.dll – Wrapper for Active Directory APIs.
6. System.Management.Instrumentation.dll – WMI 2.0 managed provider (combined with System.Management namespace in System.Core.dll).
7. System.WorkflowServices.dll and System.ServiceModel.Web.dll – WF and WCF enhancements (for more on WF + WCF in v3.5 follow links from here).
8. System.Web.Extensions.dll – The implementation for ASP.NET AJAX (for more web enhancements, follow links from here) plus also the implementation of Client Application Services.
9. System.Core.dll – In addition to the LINQ to Objects implementation, this assembly includes the following: HashSet, TimeZoneInfo, Pipes, ReaderWriteLockSlim, System.Security.*, System.Diagnostics.Eventing.* and System.Diagnostics.PerformanceData.

In addition we are adding System.Web.Extensions.dll with the LinqDataSource, Asp.NET Ajax support and asp:ListView