Cussler: About the same with me. I read a few from the Dirk Pitt series but lost interest. I'll probably cherry pick a few more as I know some of the series have been made into big movies.
Robert B. Parker: The Spenser books were the basis for the "Spenser: For Hire" TV series with Robert Urich from the mid-80s. Spenser is a smart-alack ex-cop turned PI. Some of his wise cracks are quite funny. While the plots are all very serious, Spenser's attitude about things keeps it a bit lighter. "The Godwulf Manuscript" is the first in the series and is as good a place to start as any.
Jesse Stone has a different tone to it. Stone is a homicide detective from Los Angeles with a serious drinking problem who gets hired to be Chief of Police in a small seaside town not far north of Boston. While he has to keep a close eye on his drinking, he does mostly clean up and becomes a good Chief. A number of the stories involve criminals assuming they're way better than any small town cop could be and being very surprised when they run into a very experienced detective. While Stone is certainly not devoid of humor, he isn't the wise-cracker that Spenser is. I would definitely start this series with "Night Passage", the first in the series. It explains his whole back story and takes you through how he became Chief.
My one complaint about these series is both Spenser and Stone have extremely complicated relationships with their significant others (for lack of a better term). It gets tedious.
Sadly, Robert B. Parker died in 2010. Both series have been carried on by writers who worked with Parker before his death. I've not gotten to any of the non-Parker ones so I don't know how true to the originals they are. There are nine Parker Jesse Stone novels and thirty-nine Parker Spenser novels, so quite a bit of material from the original author.