Rancho Cucamonga and Ontario are not traditional sightseeing day trips from San Bernardino, but they can be useful if your idea of a good afternoon includes shopping, restaurants or an event rather than another museum.
Rancho Cucamonga
Victoria Gardens is the obvious draw, combining a large shopping and dining district in an outdoor setting. Rancho Cucamonga also sits on the historic Route 66 corridor, so road-trip travelers can connect the visit with the wider highway story.
Ontario
Ontario is important because of Ontario International Airport and its large retail and entertainment areas. Ontario Mills is the big shopping name and can consume several hours if outlet-style retail is on your agenda.
Would I make a special trip?
For pure sightseeing, probably not before Lake Arrowhead, Redlands or the mountains. But travel is not always about landmarks. If you need shopping, want a larger restaurant selection, are attending an event or flying through Ontario, combining these cities with San Bernardino is practical.
Just remember Southern California traffic. A short freeway distance can become much less short at the wrong time.