In my particular neck of the woods, .NET development is a little dry and low-paying, while is appears Java development is still pretty hot. Contracts are going for very good rates as well.
What avenues should I take to parallel my development expertise in DotNet with Java? I'm a senior developer/architect/dba.
If you aren't already proficient in C#, I would suggest doing so.
Also, there are OS projects in the .NET world that mirror Java projects
NHibernate is one (Hibernate is the Java version) link
You might want to try looking at some of those projects and seeing the correlations. It might be a good way of showing how the two languages accomplish the same thing. For instance, how are generics handled in Java as opposed to C#?
Also, check out this comparison site.
Download the JDK and Eclipse (or choice IDE) and start playing with it.
If you are a good C# programmer, you'll be a good Java programmer, you just need to learn the Java framework.
Replicate one your existing projects in Java.
There are tons of books, tutorials, textbooks, classes, and articles about how to learn Java, but you really want to build something with it. And, a working app is going to look good on the resume.
Once you've learned the basics of the language, I would suggest digging into the source code of some existing applications and see if you can understand them and modify them without breaking them. Either Open Source, or see if a different division of your company might be using Java for something.
As an experienced developer, you presumably are already familiar with the cross-language concepts involved in both.
In java, there is a lot you could potentially learn. I suggest you do some research on the job web sites for your area to find which skills appeal the most (or pay the most money if you wish)
I suggest you get a free IDE and do a google search for examples and tutorials on the topics which you have chosen.