Too many, if any!
There are way too many areas I could really expand into and the goal posts have a habit of being overly mobile.
Currently I am looking into moving into ASP.NET MVC 3 and making (automated?) testing a bigger part of my application development. The most recent testing methodology I’ve been looking into is Business Driven Development (BDD) as opposed to Test Driven Development (TDD).
To help with BDD I have been testing out SpecFlow. This is and awesome tool for turning structured human readable requirements into actual testing code which you can compile and put through your test runner. I just think it is fantastic and makes writing unit tests so easy and even helps you by supplying you with the basic code you need to insert into your test classes and then all you need to do is fill in the logic.
For years now sadly, I have been meaning to get into testing frameworks but have found it very hard to get my head around it all. SpecFlow has begun to significantly break down that barrier.
There is plenty more areas I could go into, but ASP.NET MVC 3 and BDD/TDD are my main focus for the immediate future.