From the Wiki
Addresses can contain all alphanumeric characters except 0, O, I, and l. Normal addresses currently always start with 1, though this might change in a future version. Testnet addresses usually start with m or n. Mainline addresses can be 25-34 characters in length, and testnet addresses can be 26-34 characters in length. Most addresses are 33 or 34 characters long, though.
You'll probably want to store them in a VARCHAR. Although, if you really
want to save space, you can Base58 decode them and store them in binary without the checksum using only 20 bytes.