Yahoo!, AOL and Microsoft are just a few options-go exploring and find the provider you prefer. If possible, spring for your own domain name. It projects a more professional image and is easier to remember than a sub-domain. Credit card processing is also essential, although this is where the fees add up in per-transaction charges, merchant account charges, etc.
Access to marketplaces, whether auctions or mall-style shopping sites, can be advantageous. However, competition is likely to be stiff. Visit some marketplaces and decide whether it's worth your while to be included. Rome wasn't built in a day . . . but your online store can be.