As of June 15, 2008 American Airlines is charging most passengers $15 for checking a single bag and $25 for a second checked bag.  With the rising price of oil, other airlines are expected to soon follow suit, so a carry-on may be your best bet.   
According to the Transportation Security Administration air travelers bringing liquids, gels and aerosols through security checkpoints must place all three-ounce or smaller containers in a single, quart-size, zip-top, clear plastic bag.  For further information check out www.tsa.gov