With some googling I noticed some people were talking about a backlit Game Boy Pocket mod. I made guides for this as well as Game Boy Color and Game Boy Advance, so I just thought I'd post them here:
Someone was also selling some hilariously terrible 2-LED frontlight of a GBC.
Game Boy Pocket (note: to get the backlight from an LCD, take a broken DS lite LCD and when you replace it with a brand new one keep the broken one for its light!)
http://forums.modretro.com/viewtopic.php?f=3&t=210
Game Boy Color (technically a frontlight):
http://forums.modretro.com/viewtopic.php?f=40&t=916
Game Boy Advance (Again, a frontlight):
http://forums.modretro.com/viewtopic.php?f=40&t=72
REALLY crappy pic; you can barely see it: