You can always start with liquidation or small wholesale lots. eBay US is a good place to pick up small wholesale lots and they are a great way of getting a feel for what works and what doesn't without risking too much.
You need to research eBay and see what is selling well. Also think about possible niches related to your own interests. No one can tell you what to sell as your own passion and enthusiasm for a product makes a big difference to how well it sells. Plus the more you enjoy working with something, the more time and thought you are likely to put into it, thereby creating a better business.