Sure. It's a long list. Note that I have included the notes that were offered for why a book or story is included.

• The Dark Tower I: The Gunslinger
• The Dark Tower II: The Drawing of the Three
• The Stand (This novel is important as one of the characters from this features heavily in the series)
• Eyes of the Dragon (The same character from The Stand crosses over into this novel as well.)
• The Talisman (Although it is not extremely important, this book introduces a lot of concepts that appear in the The Dark Tower. The sequel to this book is very important (that comes later in the list).)
• The Dark Tower III: The Wastelands
• The Dark Tower IV: Wizard and Glass (You will see very quickly why it's important that you read this book right after finishing The Waste Lands)
• Salem's Lot (A character from 'Salem's lot appears later in the storyline, and this is a good place to stop and read.)
• Night Shift (Specifically "Night Surf" and "One for the Road". Although not directly important for the tower (why I marked it bonus), they tie into other books that are related.)
• The Mist (Although not extremely important, this novella provides some context for things that occur later in the series. Plus it's a short read, so worth adding in here)
• Insomnia (A very important novel to The Dark Tower series. Multiple characters appear in other books, Roland is mentioned, and concepts appear in the series)
• Everything's Eventual (Specifically the short story "Everything's Eventual". The story introduces a character that will appear later in the series)
• Little Sisters of Eluria (This novella is basically a prequel to the series. Some people think it should go first, but it follows a flashback that occurs in the 4th book. I think it's better to wait on this one until you have more context for the character)
• The Dark Tower IV 1/2: The Wind Through the Keyhole (This book is a Dark Tower novel, but it was published after the last book. Fits in between books 4 and 5. Some people think you should wait until after finishing the series, others feel it belongs between. You can choose whichever you want)
• The Dark Tower V: The Wolves of Calla
• The Dark Tower VI: The Song of Susannah
• Hearts in Atlantis (All of the stories from this book tie together. One of the characters from this collection is important in the last book. Also, similar concepts from the series appear.)
• Black House (This is the sequel to The Talisman. Very important to the series. )
• The Dark Tower VII: The Dark Tower
• Desperation (Some argue that this book should be read in the middle of this reading list, but I think it can wait until after the series. Has to concepts that are in the final three books. Definitely read this one before The Regulators.)
• The Regulators (This is the "sister" novel to Desperation. Great combination.)
• Ur (This one is only available as an e-book. Deals with the idea of the multiverse. A very good novel to link in.)
• Gwendy's Button Box (Hasn't been confirmed that there's a connection, but there's definitely a heavy implication that there is.)
• Gwendy's Magic Feather (Although King didn't technically write this one, it is the second book in the Gwendy series.)
• Gwendy's Final Task (Definitely has more of a tie into the Dark Tower series than the previous novels. )
• Fairy Tale (This book hasn't been released yet, but from the description, it will likely have heavy ties to the tower.)
• It (At this point in the list, the following novels don't contain explicit ties to the tower, but have concepts that are similar or related. The idea of a character from this book does appear in the series. )
• Revival
• Rose Madder (Mild connections to book three of the series.)
• Bag of Bones (Connections are kind of there, plus a brief appearance of a character from Insomnia.)
• The Tommyknockers (Vague concepts)
• Needful Things
• The Outsider
• From a Buick 8 (King has said it's related, so that means it's related.)

Check out the Kingslingers podcast if you haven’t already. The set up is that one of the hosts has never read any Stephen King and the other is a massive King nerd. The hosts read a few chapters and then discuss the themes and writing. The first series focuses on the Dark Tower series and then subsequent series discuss the related books. I recently re-read the Dark Tower and it added so much to my enjoyment of the writing