I have exactly the same issue. I work with a Thinkpad X220 and have Xubuntu 11.10 installed.
When I suspend my laptop, while connected to my external monitor (either cloned or only using the external monitor), it gives a blank screen when coming out of suspend. I can still see my mouse moving, but both screens remain blank.
Some further information;
I have memorized the "Display settings" command. When I press the command sequence on my keyboard to 1) show only laptop screen and then 2) show only the external screen, my display (on the external monitor) returns and I can proceed as normal. But I have to do this every time, and when I make one mistake I am lost (as I cannot see the output unless I do it completely right).
I have now enabled a dual-monitor setting, using the command
"xrandr --output VGA1 --right-of LVDS1".
Now, when I put my laptop to sleep/suspend, both displays work normally (dual) after resuming from sleep or suspend. But I do not use the display configuration then, just this command with xrandr.
I am not an expert, so I do not exactly know what the problem/solution might be. But I guess I am looking in the right direction.