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