Libraries to Try

Spring, Guice, Pico (known Java IoC containers)

FLEE

http://commons.apache.org

XSTM (update 7/7/2013)

Dynamic LINQ

SignalR

Knockout

ILOG Rules for .NET 3.0

MVC from CodePlex for analyzing and recompiling

MSMQ

http://grok.zope.org/

StructureMap

Unity, autofac

Ontology libraries

Reflection.Emit http://www.codeproject.com/Articles/121568/Dynamic-Type-Using-Reflection-Emit

Task Parallel Library

Xmi CodeDom Library

http://prevayler.org/

Grails GORM

CodeMirror

http://www.esigate.org/

http://pitest.org/