The Discworld books have quite a few different arcs, and which you'll like depends mostly on which characters appeal to you.
My personal favorites have always been the Watch books. This series starts with "Guards! Guards!", then "Men at Arms", "Feet of Clay", "Jingo", "Thud!", and "Night Watch". It focuses on life in the big city of Ankh-Morpork. They start out as detective stories, and slowly becomes more focused on the politics (Jingo and Thud are the two big ones for this). Sam Vimes, as the Commander of the Watch, is the main protagonist, along with the other members of the Watch (Carrot, Angua, Nobby, Fred Colon, and others). The Patrician, Vetinari, is also a pretty prominent character, as the Not-Quite-As-Evil-As-He-Claims ruler of the city.
The Death books are also quite good (Mort, Reaper Man, Soul Music, Hogfather). The main character is Death, and is the perennial straight man. Mort's about his apprentice, Reaper Man is about him taking a holiday, Soul Music is about the advent of Music with Rocks In (rock and roll on the Disc), and Hogfather is about holidays and their importance. The bad guys of the Death books tend to be the Auditors, accountants of reality who try and destroy all life, because we're disorganized.
I'm not a huge fan of the witches books, or the Rincewind stuff, so I'll leave others to comment on those. Lords and Ladies is a great take on the fair folk, but for the most part, I don't care about Lancre and the stuff that happens there. Rincewind is the eternal non-hero, a bumbling wizard who's always in the right place at the right time, and he HATES it. Not really my cup of tea, though.
Some of the standalone stuff is quite good as well. Carpe Jugulum is about vampires and where they come from, as well as the importance of tradition. Thief of Time is great fun with the Monks of Time and the ultimate clock, and probably my favorite one-off novel in the series. The Truth is about the Disc's first newspaper, and the problems it causes.