The R300 has a suprisingly good internal microphone along with a mic jack for an external microphone. It has much better user control over audio than any other entry level HD camcorder that I am aware of.
Yes, there is an EXCELLENT high-fidelity sterio mike built-in. It is much more dynamic than previous Canon models - I have several. There is also a mini-hot shoe in case you want to attach an optional external mike later.