Netflix gives an answer to the question “You login to a Linux server with a performance issue: what do you check in the first minute?” in Linux Performance Analysis in 60,000 Milliseconds.
The short version:
uptime
dmesg | tail
vmstat 1
mpstat -P ALL 1
pidstat 1
iostat -xz 1
free -m
sar -n DEV 1
sar -n TCP,ETCP 1
top
They provide a short discussion on each tool.
Anything else you would add?