I know just from talking to a lot of people that eBay is intimidating and a hassle at times, and some people may shy away from it. eBay is also quick to snatch a pocketful of pennies from your sale, and then Paypal steps in as the second shark to grab another portion of your sale. Sure, it leaves you with more than GameStop would, but it'd be nicer to gain the full sale price of your actual auction. So in looking for some alternatives to selling your games, I've come across Gladriel which is a mix of a community-fueled news, reviews, walkthroughs, etc. gaming site - combined with a strong auction marketplace.
It's a lot different from eBay, the biggest difference being that essentially you can actually buy and sell without reaching for your wallet. Since it's also a community gaming site, contributing various content such as news or reviews will net you diamonds.
Diamonds serve two purposes. You can use them to enter Gladriel-sponsored raffles, which run quite frequently for console giveaways and popular new games - sometimes multiple raffles running per week (StarCraft II is even up right now!). If you don't want to enter the raffles, you can convert your diamonds to gold on the site, which is the auction currency.
If you're just interested in something quick and painless and are uninterested in contributing, you can also use good ol' U.S. dollars via Paypal. The conversion rate is 1 penny = 1 gold, so 100 gold is equal to $1. Just for signing up though, youre awarded with 500 gold ($5) and one diamond.