Steam

Steam is a wonderful thing, and no, I'm not talking about what happens when you apply heat to water.  Steam is a website that allows you to buy a myriad of games online, through download.  I know you're wondering why that is so great.  Let me count the ways!

1. Steam has sales...constantly.  There are sales that run for a period of time, daily deals, and flash sales, which are really short.  Now, lots of websites have sales, but on Steam, Mark got Saint's Row the Third for only $6.*  Right now, it's $40 at Best Buy's website.  If you pay attention, you'll find great deals.  At the same time, this can be bad.  It sucks your wallet dry, but the price is oh so good.
2. If you're near a computer with internet access, you have access to your games and saves.  There is a fun little Steam cloud that keeps all your stuff together.  This way, you can log into Steam and play on your PC or laptop with little to no fuss.  Traveling?  You can use the computer wherever you're on your way to visit.
3. It's easy to use.  Some places make the download process more difficult than it need to be.  Steam is user friendly.
4. You can give someone a Steam gift card.  Need to buy a gift for that nerdy cousin of yours but don't know what games he has?  Steam to the rescue.  Want to get an inexpensive gift for someone that has the potential to result in some good product?  The Steam card is the perfect gift.  If you just don't want your kids using your checking account, you can load them up with Steam cards.
5. There are so many different games on Steam.  You have access to small, over-looked games that you may not otherwise play.  When they do bundles, you'll get multiple games for a great price.  You may find some tiny little game that you've never heard of, and you may find out that it is great.  This has happened to Mark.
6. They're selling a lot of the same first run games that you would find at Gamestop or Best Buy, and it is usually cheaper.  If you have a good gaming computer, some of those games might even play better on  your PC.  

Aside from it taking all of our money in tiny little bits, Steam is amazing.  Mark gets all the games he wants for a fraction of the price.  He has spent the last two days engrossed in a few games he bought on Steam for under ten dollars.  You really can't kick on that.  Heck, they even let you vote for what should go on sale.  Steam is awesome.

*It was part of a bundle, so he actually got a few more games for that $6.