Audiogon is great, and well worth the modest cost. You tend to get more qualified reponses. It's definitely more suited to higher end audio than to mainstream level gear.
I've had some success with Marketplace, but the noise level is high. Prepare to get a bunch of messages with the default, "Is this available". Clearly, these are from rocket scientists.
USAM is a pretty good option as long as you're willing to ship to Canada. Yes, even on the US version, this is most of your audience.