Genesis and Saint Oniisan are two irreverent gag manga about religion and god(s).
A bit of a stretch, but if you enjoyed one of these irreverent gag manga where nothing is off-limits, you may enjoy the other. Saint Oniisan mainly pokes fun of religion, while Dance! Kremlin Palace mercilessly mocks anything and everything Russian (and is much more explicit).
Nozomu Itoshiki is a high school teacher who views everything in life in the most negative way possible. Even his name reflects his personality: if the Japanese characters are written horizontally, they spell out 'despair.' One day during one of Nozomu's many suicide attempts an incredibly optimistic young girl named Kafka Fura rushes to save him from hanging on a sakura tree. Nozumu later finds out that Kafka is a student in his new class! In fact Nozomu's new class seems to be made up entirely of strange, troubled individuals who constantly foil his attempts to end his life.
Saint Young Men and Sayonara Zetsubou Sensei are parody series that mock modern Japanese society and pretty much everything else. Both are peppered with pop culture (especially references to other manga/anime).