eBay is the best to get started with just about anything. Plus people trust eBay... I don't know why? Amazon is great to set and forget, you can also sell digital stuff there. I'll have to look into some of the others.
I'm prefer to sell through ebay if you have rare items. If you have a lot of stuff, than, I think, you can use your own site to sell it.
Clickbank is also a great place to sell digital products. they also offer nice incentives to their affiliates so you could get others sell for you.
If you want to create your own "Online Store" and if you're somewhat new to getting it set up, there's the " MyOwnGoldenGoose.com Program ". It's really helpful since it's all in Video format and it shows you and walks you through how to set up the hosting, site/store, add products, and set up the payment page (plus other helpful stuff on how to promote it). Eitherway, great for newbies or people who want to promote their own products or other people's products.
As many has said, I think the best way to do it is to target a certain audience. Therefore if your country has a famous Auction site, you ought to start from there, then expand slowly.
Don't listen to anyone who's saying start your own site, they have no idea what they're talking about... Trust me, unless you would want to spend thousands of dollars in marketing and all that stuff your only option is to use an already established marketplace. I personally do not know any but that's where you would need to start.