Decants are something that people make on their own. The atomizers range from from fractions to full ounce sized, with all different designs in terms of glass, plastic, atomizer, roll on, etc.
Samples are found at any department store, you just have to ask like teflondog suggested. You can also get sample vials at places like Nordstrom or Sephora if you ask, explaining you want to try the scent before purchasing. I've done it. Other department stores may not do this. I don't know for sure since I never shop at anywhere but Sephora and Nordstrom when going brick and mortar purchasing.
Sample vials are okay, but inferior to atomizers to me. The top notes seem to lay flat and I just don't get the same experience with vials vs. atomizers.
You can also sometimes get free samples by filling out a form online. I've done this a few times. Of course, you will end up on their mailing lists.
In addition to the previous two sites listed, you can get artisinal samples from places like http://www.lusciouscargo.com
and if you really want to try some interesting scents which are oils, http://www.madini.com
sells sample packages as well.
Finally, there are minis. You'll see these for sale at places like Target and Wal-Mart. There isn't much selection, but still a way to get a small amount of travel sized fragrance for about $10 - $12. http://www.parfum1.com
also has a pretty good selection of minis for sale. I used to buy a lot from them, since it was a cheap way to try fragrances. They will run from $4 to $11 depending on size and fragrance. You can sort by that size on their site, which makes it really easy to find which scents you can sample that way. These will sometimes be splashes, sometimes atomizers. More often than not, splahes.
I'm not sure if that helps or not.