This gives a ton of information - way more that I generally ever need.
less /proc/cpuinfo
This is the tidy version.
lscpu
This is the min and max clock speed of the CPU:
cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_max_freq
cat /sys/devices/system/cpu/cpu*/cpufreq/scaling_min_freq
This is a cool command to keep track of the current CPU clock speed.
sudo watch -n 1  cat /sys/devices/system/cpu/cpu*/cpufreq/cpuinfo_cur_freq