dan brown has
angels and demons
the da vinci code
digital fortress
deception point
for starters, angels and demons is about langdon's first adventure, which is mentioned a few times in da vinci code through lines such as "its been a year since i nearly died in rome". there is no real advantage to read angels and demons first, just to pick up on a few of the background references.
now, while they are all good reads, they are all essentially exactly the same novel, with different characters placed in a different situation.
instead of a dangerous computer code, there is a meteor, instead of a harvard professor, there is a nsa agent.
that being said, i did read and enjoy all 4 books, but you really arent missing out too much if you just read the da vinci code and never hear the name dan brown again