Until version 9, pressing option+command+1 would bring up Top Sites. That does not work in version 9.
I see menu bar Bookmarks > Show Top Sites with no shortcut key listed next to it. That is worrisome.
However, in Preferences > Tabs I see an option named "Use ⌘-1 thru ⌘-9 to switch tabs". When I uncheck that, I get the old behavior of loading my top 9 favorite bookmarks instead of jumping to a tab. Because of this, I hold out hope there is an undocumented shortcut key for jumping to Top Sites.
Best Answer
Why not just add one yourself?
This adds the shortcut to the menu option: