Okay, so you've painted a bunch of paintings, maybe matted a few but they're not ready for framing. Perhaps you don't plan on framing them, you want to either sell them at art shows or give them away as gifts. Whether or not you mat them, you can slip them into Crystal Clear Bags. I love these bags and use them for my own artwork. They're acid free and lignin free and perfect for keeping fingerprints off of your art. They come in tons of sizes and you can find them easily at http://www.clearbags.com
They have a peel away strip that reveals a sticky adhesive to close and seal the flap on the bag. I prefer the ones they call Protective Closure Bags the sticky part is on the bag and not on the flap so you can easily slide your art in and out even after you've sealed it, because it is re-sealable. The ones with the sticky on the flap are great for odd sized pieces where you can fold the flap down tighter on a piece of art that is smaller than the bag.