The new modeling toolkit seems pretty robust, but I'm still a fan of the old Split Polygon Tool (before the Interactive Split Tool).
Both of these tools are still in the software, they're just not menu items anymore. To use them, type the commands either on the command line (below the Range Slider, on the left) or in the script editor. Execute them by hitting the <enter> key on the numeric keypad, or <command><enter> on a Mac. The commands are:
SplitPolygonTool
and
InteractiveSplitTool
pretty simple. I don't care for the Interactive Split Tool, but I have the SplitPolygonTool command on my modeling shelf. Of course, if you want, you can put these on a marking menu or associate them with a hotkey.