I like the free program Xplorer2. By default it shows three panes...a tree view of all drives/locations as well as two panes for directories. That facilitates the easy copy of files from one directory to another without switching between windows or tiling them. It also supports tabbing, so you can switch between multiple tabs in each pane. It's far more advanced than the standard Windows Explorer so it does takes a little getting used to. There's also a professional version if you want to unlock it's full power.
Another one you may be interested in is Cubic Explorer, which is also free. It's only been in development for 2-3 months now, so it's not a finished product, but it does support tabbing, theming, and a few other advanced features. It's not as powerful as Xplorer2, but it's a lot cleaner and simpler to use. At this time my only complaint is that it does not support the ability to right-click a folder and open it in a new tab. The nicest thing about it, though, is that if you choose the installer-free version, you don't have to install it, meaning you can run it from a flash drive wherever you go.
Hope this helps,