you can use them as normal i/o's too, but with stuff like spi and 74hc595 ic's you can have "unlimited" ammount of outputs.
there are ofc ic's for inputs too. pcf 8574 for example can do both in and out-put and uses i2c.
both ic's i mentioned are aviable in dip packages, very cheap and easy to handle (there are also drivers for it, like netmf toolbox and some others)