These are the shortcuts that I use all the time.
control+shift+W Wrap current selection in <p> tags.
fn+delete or control+d Forward delete. Useful for removing unwanted auto-completions.
control+shift+V Validate syntax.
command+E and command+G Copies selection to clipboard and finds next occurrence of the string, respectively.
Moving through files
command+1 through 9 Traverse the tabs in your project.
command+option+< or > Same as above, stepping left and right through the tabs.
command+T “Go to File” search box opens. Type file name for quick find.
Click on the gutter of any line to add a bookmark to that line. A star icon will appear in the gutter. Now, after you’ve strayed from this undoubtedly important line of code, press F2 and your caret* will jump to that line. You can add as many stars to the gutter as you want, and repetitively press F2 to jump through them.
*fun fact: The blinking-cursor-prompt is called a “caret.”
And of course, the textmate manual has great, easy to read documentation, covering much more.