Though Hamlet's "To be or not to be" speech is his fourth soliloquy, many websites call it his third. They're skipping the twenty-line speech that follows his interview with the Ghost, which in my view is a particularly bad mistake since Hamlet's monomaniacal vow there is at the heart of his tragedy. The internet's cosmic sinkhole of misinformation will never be filled, but it's worth throwing some dirt in when we can, so here's an accurate list of Hamlet's soliloquies, with a short description of where they occur and what they say, along with a few observations.
Robert Viking O'Brien on Shakespeare, Movies, and Books