Here are the things that are burning in my head these days, screaming at me to go through them and grok them to a point where I don't feel stupid talking about them too much:

• NHibernate+ ActiveRecord and LLBLGen
• Try to see if you can implement Hibernate Shards in NHibernate
• Spring.NET
• BOO and Boo DSLs
• Windsor Containers
• MVC and MVP patterns implemented in .NET
• Ruby and IronRuby\Ruby in Steel (whatever works for .NET)
• Take a good look at RetLang\Erlang
• F#
• Pex (when it comes out)
• WCF\WPF in depth