I was curious, since I have been watching the "100 Films To See before You Die" and so many older films seem to clock in under 90 minutes (to be sure there are plenty of exceptions).

Just a handful of films under 90 minutes:

"Toy Story", "High Noon", "Rashomon", "This is Spinal Tap", "Frankenstein" (and "Bride of"), "Umberto D", "My Neighbor Totoro", "Run Lola Run", "Duel", "Rope"...