I mostly sell books on eBay; sometimes I sell stuffed animals.

I used to sell trading cards like Pokémon, Star Wars, Magic: The Gathering, and Yu-Gi-Oh! cards. I also sold some computer items, but not so much anymore.
I started by using Amazon to sell items, but I realized that they don’t reimburse you very much for shipping, so I stopped using them. I much prefer using eBay now.
I would like to give reselling a try, as I have heard it’s quite profitable depending on the market.