Once your contract has expired you may list with anyone you choose. The agent is not entitled to have the property on-market for the full listing period, but rather has the right to sell it and receive compensation during that whole period.
On a personal note I have had success selling in the slow market by marketing heavily and producing stellar websites. Take a look at my website below to see a few examples if you like. I have had three properties sell in less than 3 weeks in the past few months.