FbGrab is a screen grabbing utility for GP2X released by Efegea.
It's an script that launches "fbgrab" executable and outputs a file named fbdump.png 10 seconds after running the utility.
I don't have my GP2X yet, so it's a pre-alpha-beta-gamma version. Yes, it's not great but will be improved when I get my unit. No overwriting previous screenshots and instead of 10 seconds, a trigger, like "L+R+Select" to take the screenshot, are features to be expected. But I no promise anything
You can download it here.