To be a bit anal...
The 737 is so far the most built commercial jetliner - the 8,000th 737 was delivered a week or so ago. There were other large aircraft that more were built, for example there were over 12,000 B-17s built. It could be argued that the 737 is the most built airliner, depending on how one counts the DC-3. There were something like 16,000 aircraft of the basic DC-3 design, most were built as C-47s, although many were converted to airliners after WWII.
