What else could it be? What should I look for?

Engine is turning over, the starter is fine. Rent/borrow a fuel pressure gauge from a parts store and check pressure at the regulator. Check to make sure you're getting spark to all the plugs. Use a timing light to make sure that spark is properly timed. Check the air gap on the crank and/or cam sensors. My reference materials don't mention a Pontiac 1000 for model year 2000, so I can't give you any gap distance values or electrical measurement readings for the sensors. The model years I do show 1000's for show them in the 80s, which means they have distributors. Make sure the cap and rotor are in good shape. The ignition control module may be defective.