Disk Inventory X will feature a new "Selection List". This list shows all files of a specific kind or all kinds (then all files are shown). The selection list can be opened by selecting a menu item or by using the kind statistic's context menu:

The selection list resides in a new drawer at the bottom of the window. The selection in this list is synchronized with the treemap and the files view. You can search for files with an iTunes-like search feature:

The kind can be choosen with the popup button above the selection list: