SharePoint have a nice way to organize your files in document library by using folders, just like Windows Explorer does. But it lacks one important feature, the treeview browser. That's what I need in my last project requested by my client. I found great SharePoint Document Library TreeView Browser WebPart, called SharePoint Stramit Document Library browser , made by Renaud Comte, Microsoft MVP. And the best part, it's free :) You could see the source code given by Renaud Comte too in the CodePlex.
There are 3 kinds of treeview here (the description quoted from CodePlex):
1. Static TreeView ,a simple TreeView WP load in one shot the document library hierachy
2. Dynamic TreeView, for large library, the loading append when you open a folder
3. Multiple TreeView, This WebPart load automatically all the document library on your local WSS site. It's a derived version of the dynamic treeview, so not big problem if there some huge lists.
To use it, just use stsadm.exe utility (read Sean Chase tutorial here, see point 22). Here are some screenshots from the CodePlex. All the credits go to Renaud Comte. Cool and great job!