Android - Why does my screen turn itself ON?

You already pointed to the correct lines -- the interesting ones are the two immediately before it:

10-01 18:25:44.391 V/AlarmManager(  279): sending alarm Alarm{40d4f110 type 0 com.gau.go.launcherex.theme.GalaxySTheme}
10-01 18:25:44.391 V/AlarmManager(  279): pending wakeup alarm com.gau.go.launcherex.theme.GalaxySTheme
10-01 18:25:44.411 E/power   (  279): *** set_screen_state 1

So GoLauncher GalaxySTheme had requested a wakeup. I've read about similar issues before on another site with other GoLauncher components (cannot remember which ones it were -- but it were some I don't use myself). In your case, there seems to be something special with the Theme used. I take it you explicitly installed GalaxyS GO Launcher EX Themes (compare the apps package name in this url with the log message quoted above: Yes, this is the one having requested the wakeup). You could try to (temporarily) deactivate/remove this theme and see if this helps.

Check if that happens with different launcher, if it doesn't you can try go launcher again with a different theme.