External drive for Mac Mini?

The optical drive in my son's Mac Mini died -- it probably ingested too many peanut-er encrusted disks. I took it apart and got the old disk out, but the drive itself appears to be toast. Lots of loud buzzing and grinding noises. Rather than pay for a new internal drive to be installed, I'd like to just hook up an external drive so he can use that. Any recommendations? Thanks!