RSA:
ssh-keygen -lf /etc/ssh/ssh_host_rsa_key.pub
Shell script which lists all public keys (RSA,RSA1,DSA) and outputs their fingerprints:
#!/bin/bash
for key in /etc/ssh/*key.pub
do ssh-keygen -lf $key
done
Tip
On Ubuntu and OS X the fingerprints can be also list by:
ssh-add -l