I've had my best success selling things on eBay with auctions that start at $1.00 with no reserve. I was going to put a $75 buy-it-now on a pair of Definitive Technology surround speakers and they ended up selling for over $200!
Just be sure to take plenty of pictures and describe any defects in the speakers in detail. Also, try and end the auction on the weekend in the evening, around 9-10pm or so.
Trust me, they'll sell for what they're worth. There's enough people on eBay these days that you'll get what you want for them, and maybe more!