Yes, I mean the ones that cost about $5 and come with the little straws that you can put on the nozzle.

Those cans of compressed air.

Because of one can of compressed air, I was able to get an XBox 360 for $25, along with Unreal Tournament III and Soul Calibur IV (which was an additional $15, but I bought that from another friend).

The aforementioned 360 belonged to one of my hallmates, and had an issue where it would play games, but about ten minutes into the game, it would stop reading the disc (bringing up an error stating the aforementioned error). We just figured the lens was dirty, so I took it to my room, ejected the tray, and attempted to clean it with the can of air.

Turns out, it's working fine. And, since my friend was already planning to buy a 360 Elite for Christmas, he had no problems with selling it to me.

Only issue I had was getting the scratchy UT3 disc to display map textures right, which was fixed after cleaning it (well, as far as I know. Meh, I know a place that can cure that). If Resident Evil 5 is working fine, I'm calling it good for now, and $25 isn't that big of a loss.