First, I suggest that whatever poster you're using, you buy two of them. One of the posters you will keep intact, and the other you can make into swatches. Sometimes it's nice to have your colors still displayed as a poster.
At Dharma's they have these two posters available:
Fiber Reactive Dyes
Acid Dyes
Depending on your craft, whether you use glazes, paints, or dyes, often times you can even find free brochures that have color swatches printed on them.
The first thing I do to my poster is have it laminated to enhance the durability of the swatches. If you don't have access to a laminator or it's too expensive to have done, I have some other tips for you which you can do later.
I then draw lines across the poster in between the swatches. I measure carefully to make sure the lines are evenly spaces so that my swatches will be the same size.
For my project, my swatches were 1 3/8" tall and 1 5/8" wide.
Next I cut the poster into long strips following the lines I drew.
I finally cut the strips into individual swatches.
*I you haven't laminated your poster yet, now might be the time to do it. You might be able to fit trimmed-down strips or individual swatches into a smaller laminator. The benefit is that all sides of your swatches will be sealed, making them a little more water proof. The drawback is that you have to cut them out again! If you're looking for a cheap hack, use packing tape. Unroll a length of packing tape sticky-side up, and place your swatches on the tape. Unroll another length of tape and carefully apply to the other side of your swatches. Now you can cut them up again!*
To keep all the swatches organized, I decided I wanted to keep them on a keyring. I punched a hole in the corner, not less that 1/4" from the edge.
I used the first swatch as a template for marking the location of the holes on the remaining swatches so that they would sit evenly on the keyring.
After all the punching, I discovered a secret. The hole makes a nice window to see how colors look together!
Don't attempt to secure your swatches with a traditional spiral keyring; you'll damage the holes! Either use a threaded key ring, a hinged key ring, or a small decorative carabiner like I did.
Now you have all of your swatches protected, organized, and ready to play with!