Ninjouzata said:
Sorry I have no experience with discus, but I would think any plants would work, as long as you have the appropriate lighting for them?
Tankmates as long as they are peaceful and can't fit in the Discus' mouth, again, I'm assuming.
Of course someone please correct me if I'm wrong but I don't think Discus belong in a 40g tank
As far as plants go, there are actually quite a lot of common plants that will not work because they don't do well at the high temps discus need. I've had success with sword plants, crypts, anubias, mosses, vallisneria, limnophilia sessiflora, etc. Basically just do some research and see what kind of plants you like a look of, and check the temp requirements. A lot of this will be trial and error, but there are certainly a lot of plants that don't do well with the temps.
As far as tank mates, that will again limit you, first because of the higher temps, and also because of the tank, etc. Cardinal tetras are great, as are rummeynose tetras. I have a breeding pair of discus that I keep with cardinals, german blue rams, hatchetfish, and a bristlenose pleco. I keep my temp at the low end for discus, 82F, but they do just fine and lay eggs every other week at least. Avoid a lot of the other tetra species like neons because many of them are too small, and will be eaten. And as DTD stated above, you definitely need a confirmed breeding pair, not just two discus. OP, I am assuming that you are buying a pair of adult discus, because trying to grow two juvi's in a planted community is pretty much a no no...
BTW, a 40G is a little bit on the small side. You really want to be looking at a 55 at least. You could definitely have a breeding pair in a 40G short term, but they really need a bit bigger space, they can get quite big!