How to find out the machine ID on various UNIXes

It recently came up that it would be helpful if we had a cheat sheet to find out the machine names for any given UNIX. I knew these off the top of my head but it would be great if people added more as comments.

HP/HP-UX: /bin/uname -i
IBM/AIX: /bin/uname -m
SGI/IRIX: /sbin/sysinfo -s
Sun/Solaris: /usr/ucb/hostid