I've used AU Lab to pipe my microphone input through my headphones, which is apparently how professionals like to record audio (a "monitor" so you can hear how you sound), but I couldn't get used to it
How was the latency when you last tried it? Most outboard audio interfaces (even inexpensive ones like the Focusrite Scarletts with ≤ 2 inputs) have a "direct monitor" feature that is as close to zero-latency as you can reasonably get.