eBay ( EBAY) is another large-cap name that's been on fire in 2013. Since the start of the new year, shares of the online auction site have climbed more than 11%. And if this firm's Rocket Stock moniker is any indication, investors haven't missed the boat on eBay yet. eBay operates the largest online auction Web site in the world, helping more than $69 billion in merchandise trade hands last year alone. That number is growing too. eBay has been expanding the footprint of its Marketplace offerings, gaining exposure to emerging markets, where the firm is going to find the majority of new users. But don't let the name fool you. eBay's eponymous auction site isn't its most exciting income source anymore. Almost 50 cents of every dollar eBay made last year came from its payment network unit, PayPal. PayPal is a unique name in the fast-growing global payments business. The network boasts more users than some conventional payment card brands, and it's accepted at more than half of all online retailers. The real growth opportunity for PayPal comes in brick-and-mortar retailers, though, where PayPal is seeing an expanding presence. With a rising tide likely to keep lifting all ships in the payments business, PayPal is well-positioned to keep growing quickly -- especially in emerging markets where consumers aren't as invested in conventional plastic payment cards. A huge $8 billion net cash and investment position on eBay's balance sheet gives the firm plenty of options right now. As long as management can avoid overpaying for acquisitions, investors should be rewarded.