A number of online commercial services provide access to Delaware case law including Bloomberg Law, Lexis and Westlaw. Reported cases from the Court of Chancery and the Delaware Supreme Court are printed in Atlantic Reporter.
Unlike many other jurisdictions Delaware unreported cases do have some precedential value ("An unreported decision, while entitled to great deference, is not necessarily stare decis"). See Aprahamian v. HBO & Co., 531 A.2d 1204 (Del. Ch. 1987).
Unreported opinions are those that have not been officially published in the Atlantic Reporter. They can include letter opinions, trial rulings and occasionally oral trial rulings.
Unreported opinions can be found on Fastcase, Lexis, Westlaw, Bloomberg Law and on the Delaware courts' website for cases after 2000. Widener Law Library has a collection of unreported Chancery and Supreme Court cases in paper. The collection covers the early 1970s to 2003.
Delaware corporation law disputes are heard in the Delaware Court of Chancery and appealed to the Delaware Supreme Court. Both courts have websites where you can find opinions dating back to 2000.