I've been asked recently for the list of namespaces that will ship with .NET Compact Framework 3.5, so here it is:

Namespace
Microsoft.ServiceModel.Channels.Mail
Microsoft.ServiceModel.Channels.Mail.WindowsMobile
Microsoft.VisualBasic
Microsoft.VisualBasic.CompilerServices
Microsoft.Win32
Microsoft.WindowsCE.Forms
Microsoft.WindowsMobile.DirectX
Microsoft.WindowsMobile.DirectX.Direct3D
System
System.CodeDom.Compiler
System.Collections
System.Collections.Generic
System.Collections.ObjectModel
System.Collections.Specialized
System.ComponentModel
System.Configuration.Assemblies
System.Data
System.Data.Common
System.Data.SqlClient
System.Data.SqlServerCe
System.Data.SqlTypes
System.Diagnostics
System.Diagnostics.CodeAnalysis
System.Drawing
System.Drawing.Drawing2D
System.Drawing.Imaging
System.Drawing.Text
System.Globalization
System.IO
System.IO.Compression
System.IO.Ports
System.Linq
System.Media
System.Messaging
System.Net
System.Net.Sockets
System.Reflection
System.Resources
System.Runtime.CompilerServices
System.Runtime.InteropServices
System.Runtime.InteropServices.ComTypes
System.Runtime.InteropServices.CustomMarshalers
System.Runtime.Serialization
System.Security
System.Security.Cryptography
System.Security.Cryptography.X509Certificates
System.Security.Permissions
System.Security.Policy
System.ServiceModel
System.ServiceModel.Channels
System.ServiceModel.Description
System.ServiceModel.Security
System.ServiceModel.Security.Tokens
System.Text
System.Text.RegularExpressions
System.Threading
System.Web.Services
System.Web.Services.Description
System.Web.Services.Protocols
System.Windows.Forms
System.Windows.Forms.Layout
System.Xml
System.Xml.Linq
System.Xml.Schema
System.Xml.Serialization
System.Xml.XPath
System.Xml.Xsl