If you've got a tank with smaller fish, and some patience just buy some amano shrimps as soon as you can.
They grow to a good four or five cm long, and are pretty chunky (especially the females). They live for many years after they reach that size. (My biggest one (named Moth-Ra) is about five years old.) Actually, there are two Moth-Ras, both females, same age age, and both still constantly covered in eggs. I wish I had the time and patience to raise the eggs, but all that salt water malarkey is just too much for me. Also, I'm sure the fish appreciate the regular feasts when the poor little blighters are released every couple of weeks!
Try and see some mature amanos if you have any mates who keep them - I have never kept discus, but their mouths don't look that big to me.
I keep about 15 amano shrimp with 6 large discus, they don't seem to bother with them as long as they're well fed. Being in a well planted tank with wood there are plenty of places for them to hide where the discus couldn't get to them but they've never seemed bothered. Discus do love tiny snails though & often I hear them pecking them off the glass!
I've read that Amano shrimps have different temperature requirements and that they cannot tolerate the high temperatures of Discus. For those of you keeping both in the same tank what temperature do you keep it at?
Since we're on the topic of Discus companions, how well do Otocinclus and Green Tetra's fair?
They'll definitely try to eat whatever they can. Despite not being aggressive, discus are highly partial to live food which means anything smaller than their mouths and moving. With that said, if you choose adult sized Amanos, close to 1" kind of sizes, and provide lots of hiding places, you should be fine.
Discus don't have the mean streak of puffers so they won't actively go all out to kill your shrimps.
Fish have color vision and according the LFS discus breeder i regularly visit, he says they will hunt shrimps with red colors.. Discus seem to be very attracted to the color red and go specialy bonkers over blood worms and or tubifex etc.. Thus any small sized shrimp with a red color is likely to be recognized as a possible food source and no go for a discus tank. Any other type of shrimp is a gamble could work could not work...