QTTabBar from QuizoApps is the best little software surprise this year for me. It adds tabs to Vista and (!) XP folders. It adds customized buttons to the toolbar. It is a huge usability boost to file management. And it is free. recommend it for everybody.
But wait, it is not over, QTAddressBar adds Vista style Folder path navigation to XP machines. Since I still have XP on my UMPC and corporate laptop, this is a very welcome extra too.
Here are some screen shots of other useful features that it adds.
1) Folder preview tip in file pane and 2) on tab bar and 3) the highlighted gridlines in details view.