There are a couple I keep forgetting to remember:
ctrl-s
freezes the screen and stops any display on the screen from continuing
(equivalent to a no-scroll key) (sometimes takes a moment to work)
ctrl-q
un-freezes the screen and lets screen display continue
ctrl-c
interrupts a running program
ctrl-\
same as ctrl-c but stronger (used when terminal doesn't respond)
ctrl-z
suspends a running program (use the fg command to continue the program, see section Controlling Jobs)
ctrl-h
deletes last character typed
ctrl-w
deletes last word typed
ctrl-u
deletes last line typed
ctrl-r
redraws last line typed
ctrl-d
ends text input for many UNIX programs, including mail and write.
(Originally from this page.)