I have a thinkpad running Ubuntu on it. Whenever I suspend and resume again, the touchpad no longer works.

To fix this, one has to call following as root to reload the kernel module:

modprobe -r psmouse
modprobe psmouse

Alternatively, this can be automated with a script.
Place the following code in a file called

/lib/systemd/system-sleep/fix-touchpad

#!/bin/sh

PATH=/sbin:/usr/sbin:/bin:/usr/bin

case "$1" in
   pre)
       #code execution BEFORE sleeping/hibernating/suspending
   ;;
   post)
       #code execution AFTER resuming
       /usr/sbin/modprobe -r psmouse
       /usr/sbin/modprobe psmouse
   ;;
esac

exit 0

And don’t forget to add execution rights to it using

sudo chmod +x /lib/systemd/system-sleep/fix-touchpad