I have an Mac Mini from 2011. Sometimes (I would say 80% of the time) when I wake up the monitors, after they've been sleeping, my main monitor (a Benq G2220HD 22″, connected via DVI → Mini Displayport) wakes up with just noise. Its like a grey background with black, white, red, green and blue dots all over. To solve this I have to power off the monitor, and power it on again.
I also have a second monitor plugged in, through the included DVI-HDMI adapter (doesnt make a difference if I hook up my Benq using this method.) The second monitor works fine (I can see/use it while my other one is messed up), but it will also get the same issue if it is the only monitor hooked up.
I'm running OS X 10.8.5 (this was also on Lion and all other versions I've tried), I've done a SMC reset, and I've updated the EFI to MM51.0077.B10, which is said to fix an HDCP authentication thing, but it doesnt fix my problem.
My current solution is to just never sleep the monitor, instead have a screensaver running, but I want it to sleep because it gets really hot otherwise.
This doesn't happen in Boot Camp (Windows 7). It works fine there, so it has to be something with OS X I'm thinking.
UPDATE 26-10-2013 : This still happens in 10.9 Mavericks.