There are:
1,461,501,637,330,902,918,203,684,832,716,283,019,655,932,542,976 possible bitcoin addresses.
As ribuck says, that is a very big number. There are approximately:
133,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000,000
.. atoms in the Earth, so even if you used just 100 atoms to store each bitcoin address, you'd run out of atoms before you were done generating addresses.