Obvious free agents are Abdul Osman, Prince Buaben and Jim O'Brien. They all scream of "couldn't get main target, fall back on experienced obvious option" though.
A wildcard would be Diego Poyet, who seems to be a free agent and apparently been km trial at another Scottish club, I've forgotten who though, although he seems out the budget.
Am I allowed to suggest this is the type of position we should be paying a fee for? Spend £100k on the perfect player in his mid-20s seems to make a lot of sense, and deep playmakers generally don't cost as much as game changing attackers.