From the theory of highly dynamic systems and chaos, perfectly classical and in principle deterministic systems can exhibit a behavior, where minute perturbations of the initial conditions are exponentially enhanced over time, and thus arbitrarily small perturbations can, after a finite time span, lead to a state that bears no resemblance at all to the evolved state of the unperturbed system.
Of course, this system is deterministic if you know all the initial conditions exactly. Not just to high precision, but exactly. But that would generally (since the rational numbers are not a dense set and therefore have zero probability to be occurring exactly in a real-life setting) require an infinite amount of information, which is of course impossible - so your system is really, fundamentally unpredictable, although still in principle deterministic - this is pretty much the definition of "chaos".
According to people more clever than me, quantum mechanics is also deterministic, by the way - see the question that @Greg links to in his comment to your question.
I do not know if that rules out "free will", because I have never seen a consistent and coherent definition of what "free will" is, but it should be clear that it leaves ample room for complexity and unpredictability.