I have large hand blown glass bongs that are too beautiful to stay dirty so I picked this up today.
http://theoriginalbuddy.com/
I am impressed with how well it works. Makes cleaning the inside of a bong, that has some crusted resin, a breeze. It also comes with a super small magnet to clean the inside of those hollow glass bowls.
If your bong has a ice catch beware that if it's not a fairly large bong this brush may not fit past it.