I'm working on a sweet project at the moment using both WPF and WF. One of my custom activities has a property of type Type, where it would be cool for the user of the activity to be able to use the designer to select a type, just like what happens in the WF designer when I choose a type. However, no type picker popped up.
So I went googling and found that Daniel Cazzulino also ran into this problem and created a fantastic little project to harness the power of the real WF typebrowser. He writes about it on this blogpost and later moves the project to code project. You can find the article and his download code here.
However, as you can read in the comments, something was broken. Looking through the code, although small, made me not want to waste time on understanding the System.ComponentModel namespace in that much detail at this point
(although, when working with WF, you will soon need to customize property pickers, so I will have to look into it someday soon).
Daniel himself points to the Patterns and Practises entlib library: they offer the same functionality. I downloaded their sourcecode, and I'm quite sure they just used Daniels code and improved upon it a bit. However, with all the Entlib references, the project felt a bit heavy.
What I have done is rip out all the references to entlib that I do not care about, used a few files from Daniels original solution and worked around a few shortcomings. Nothing fancy, I just hacked at it until it worked.

Now, since I have used some code (without license) by Daniel and code by the Entlib group, I'm not sure if I can publish a derivative without getting into problems. However, I've read their license, and I think it's okay.
You can download the project here, don't ask for changes because I'm not interested in spending more time on it. All credits go to Daniel.
(Also, find out how to create your own typefilters in his post).
Have fun with it. Leave a comment if you find it useful.