For MySQL 5.0.3 and higher, you can use BIT. The manual says:
As of MySQL 5.0.3, the BIT data type is used to store bit-field
values. A type of BIT(M) enables storage of M-bit values. M can range
from 1 to 64.
Otherwise, according to the MySQL manual you can use BOOL or BOOLEAN, which are at the moment aliases of tinyint(1):
Bool, Boolean: These types are synonyms for TINYINT(1). A value of
zero is considered false. Non-zero
values are considered true.
MySQL also states that:
We intend to implement full boolean
type handling, in accordance with
standard SQL, in a future MySQL
release.
References: http://dev.mysql.com/doc/refman/5.5/en/numeric-type-overview.html
BOOL and BOOLEAN are synonyms of TINYINT(1). Zero is false, anything else is true. More information here.