Here are the official Google Wave keyboard shortcuts. They can be found here.

Shortcut Key
Action
Navigation
Up/Down Arrows Arrow keys allow you to navigate through messages in your account.
Home Takes you to the first message in a wave.
End Takes you to the last message in a wave.
Space Takes you to the next unread message in a wave.
Left/Right Arrows Switches focus between the compose window and the inbox.
Page Up/Page Down Takes you to the next page within a panel.
Ctrl then Space Marks all messages “read” when focus is on the Wave panel.
Messages
Enter Reply to a message at the same level of indentation.
Shift then Enter Reply to a message at the end of a wave. The new message will appear at the same indentation level,at the very end of the wave.
Ctrl then E Edit message.
Text Editing and Formatting
Shift then Enter Same function as ‘Done’ button — signifies you are finished editing your addition to a wave.
Ctrl then B Bolds/unbolds selected text.
Ctrl then I Italicizes/unitalicizes selected text.
Ctrl then K Adds a link.
Ctrl then [n] Makes the current line a heading, where [n] = 1 through 4 for different sized headings.
Ctrl then 5 Adds bullets.
Ctrl then 6 Removes formatting from text.
Copying and Pasting
Ctrl then C Copies the selected text.
Ctrl then X Cuts the selected text.
Ctrl then V Pastes the text you have copied or selected.
Shortcut Key
Action
Navigation
Up/Down Arrows Arrow keys allow you to navigate through messages in your account.
Home Takes you to the first message in a wave.
End Takes you to the last message in a wave.
Space Takes you to the next unread message in a wave.
Left/Right Arrows Switches focus between the compose window and the inbox.
Page Up/Page Down Takes you to the next page within a panel.
Ctrl then Space Marks all messages “read” when focus is on the Wave panel.
Messages
Enter Reply to a message at the same level of indentation.
Shift then Enter Reply to a message at the end of a wave. The new message will appear at the same indentation level, at the very end of the wave.
Ctrl then E Edit message.
Text Editing and Formatting
Shift then Enter Same function as ‘Done’ button — signifies you are finished editing your addition to a wave.
Ctrl then B Bolds/unbolds selected text.
Ctrl then I Italicizes/unitalicizes selected text.
Ctrl then K Adds a link.
Ctrl then [n] Makes the current line a heading, where [n] = 1 through 4 for different sized headings.
Ctrl then 5 Adds bullets.
Ctrl then 6 Removes formatting from text.
Copying and Pasting
Ctrl then C Copies the selected text.
Ctrl then X Cuts the selected text.
Ctrl then V Pastes the text you have copied or selected.