I am wondering if there is an auction website like ebay, or anything similar that accepts bitcoins.
And please can you tell us what is demand? Because if you are looking for wide options, there is nothing that can change ebay and if you want to sell something, I highly doubt you'll achieve huge audience for your product, currently nothing can change ebay. But if you own for example Casascius physical bitcoins, then this forum is amazing place to sell too because a lot of people buy and sell it through auction.
Since nothing can take place of ebay as for now, better to exchange your fiat into bitcoin.