There are quite a few.
The University of Nebraska Medical Center shares one or two residency programs (ortho, i think) with Creighton, so some students might rotate through there a few times. It's a huge medical center with tons of research and tertiary care specialties. Their liver/kidney/pancreas/small bowl transplant program is huge.
Luthern Immanuel is another hospital where students do a psych rotation.
There's also Methodist and Children's Hospitals.
The VA is another.
Finally, Bergan Mercy is one further west where students may rotate.
There may be one or two I've missed, but you get the idea. All these affiliated hospitals definitely compensate for Creighton's smaller medical center.