Grew up with his books and really enjoyed his writing. After Stephen King he was probably the first author whose books I sought out to read. Wish they could actually get his books right in a film.
They're all the same, but I would say Sahara, Inca Gold, or Atlantis Found are starts. Really, just look for one that is based around some historical thing that interests you and start there.
Raise the Titanic got him his first recognition. Enjoyed Dragon, Treasure and Cyclops. Basically its main character is James Bond meets Jack Ryan meets Indiana Jones. Cussler was also a real life badass.