Here’s a list of what can be refunded and how…
Games – Refundable within 14 Days of purchase. If the game has less than 2 hours on it.
DLC – Refundable within 14 Days of purchase if the underlying title was played for less than 2 hours.
In-Game Purchases - Refundable within 48 Hours as long as the item hasn’t been consumed, modified, or transferred. (Applies to all Valve games, 3rd Party Devs have option to enable Refunds)
Pre-Orders - Refundable anytime until the game launches, on release you can still get a refund within 14 days, as long as the title has less than 2 hours of playtime.
Wallet Funds – Refundable within 14 days as long as the funds haven’t been used.
Bundles – Refundable within 14 days as long as the playtime on all items in the bundle are less than 2 hours combined.
(It should be noted that all Refund options need to go through Steam Support.)
Now for the flip side, here is what can’t be refunded.
Purchases Made Outside of Steam – Obviously.
Games You Have Been VAC Banned From – Don’t turn on your wallhacks in Insurgency and expect to get your money back.
Movies – With films bought on Steam, there is no Theater for you to throw your popcorn and drinks around when you realize you can’t get a refund.
Gifts – It’s too late to give back Bad Rats.
If you want to look further into the Refund Policy on Steam, check out the Steam Store page.
As for Spore? It looks like I’ve owned it for too long and have played it too much to get a refund. Darn.