ALT+W selects the Roto Brush tool. Like other tools, the short cut either delves into the tool's variation with no toggle available. Instead, you either click on another tool or hit the short cut key for another tool.
BTW, you can use the 1 and 2 keys on the main keyboard to move back and forward repectively - this is much more useful that the PAge Up/Page Down keys which is situated towards the left of the keyboard.
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From memory you used to be able to cycle through all the bezier tools using the 'G' key, but they changed that in CS6. I can't imagine why they did it (unless they wanted to draw attention to the new variable feather tool) - as it really slows me down not having the shortcut. Is there a way to map your own shortcuts to alter this?
Aha - I've found it. If you go to your preferences>General there is a tick box that says 'Pen shortcut toggles between Pen and Mask Feather tools'. Untick this and your 'G' key will toggle through all the pen tools.