There are self inking stamps, (The ink pad is hidden inside and automatically inks the stamp; you will need to replace the pad every so often.)

There are heavy duty metal and light weight ABS plastic versions. There is also a small one often used on loyalty cards.

The traditional ink pad needs a separate pad as well, various colours of ink are available.
Water proof ink is another option. The latter is often used to mark tyres for safety purposes. The pads can be replaced, the stamp text/graphics can also be replaced.

Date stamps are another option, the date is adjustable.