Quite a few options to consider, but when you evaluate the traffic part of the selling equation I doubt if anything is going to come close to ebay, and if it did then they would be forced to look at their pricing structure more carefully.
The fact that they don't indicates that they are confident about their place within the market.
I would think that it's a smart move to take advantage of the alternatives, especially where listing is either inexpensive, or free. Lets face it, everyone can't just sit around complaining about other sites not having traffic flow if you are not prepared to help them to grow by putting your products there to start with.
It's a two edged sword, traffic can generate more products, but product range can also generate traffic, and as sellers you have that power to control that aspect of the equation.
Serious alternatives as we currently stand, everyone seems to have a favourite, but Yahoo seems to me to be in the best possible position to offer a serious alternative to ebay, but like I sad.....try and spread them around, it can't hurt!