Discus compatible tankmates?

What do you feel are 100% safe tankmates?
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What do you feel are compatible tankmates with caution and why? Please explain what problems may occur with the non 100% safe but still compatible tankmates.

I get questions like this every now and then and so far I've been suggesting plants and snails. I've seen them mixed with juvenile angelfish but I'm sure once the angelfish pair up and lay eggs. That they will become aggressive and no longer safe for the discus. How about neon tetras? They never bother anyone, but will they get eaten by the discus? I want to hear about your experiences and opinions. Please include whether you have experience with a certain combination or if you believe that a combination will work but have no personal experience doing it. If possible, for the personal experiences please include how long you successfully kept the combination together. As mentioned above, the angels work but not for long. So juvenile combinations are not a sure thing to work out long term.

I've been keeping Discus for about 3 years.  Heavily planted 150 with typically 8-10 Discus in it.  Tank mates I've had success with are both Bolivian and German Blues.  Cory's and plecos and guppies and assorted tetra's.  I've had angels in with them but angels are more aggressive feeders and can over compete for the food.  Discus are known to like grazing off the substrate but I've not experienced that... Mine are pretty aggressive eaters and smack the water surface as I'm feeding them but the Angels will pester the Discus once reaching adult size.  
Note:  I've had Bolivian Rams, German Blue Rams and guppies spawn in with the Discus.. 
Bill

I have kept discus for a short time and their beauty is unparalleled to anything I have ever kept.   I have never mixed angels with discus because of what I read and Bill's statement about getting out competed from aggressive eaters. Discus are known to be slow eaters compared to fish like angelfish and other cichlids. From what I have read and seen cardinals tetra, neon tetra is  100% safe. I have listed a basic guideline for keeping discus ; tank mates, Plants, food, tank size and temperature. Please feel free to add to the list. (This information is only my opinion based on my experience and research)

Tank size.
Minimum- 55
Maximum- as big as you can get.

Schooling fish.
Neon tetra
Cardinal tetra
Rummy nose tetra

Cichlids
Apistogramma
Rams

Cleaners.
Ortocatts
Corries
Plecos
Snails
Bamboo shrimp( mostly for looks)

Plants. (Some beginner plants)
Amazon sword
Crypts
Jungle vail
Java moss
Java fern
Cobamba

Food.
If you want to keep your discus healthy you have to add variety and good amount of protein in their diet.

Frozen Beef heart or flake
Frozen bloodworms
Frozen brine shrimp
High quality flake
Pellets
Freeze died food

Filtration.
Like any fish keep your nitrogen cycle in check and keep up a good water change schedule.
Ph-
Constant ph is better then unstable ph. I have kept and breed discus at 7.6.  

Temperature.
82-86 degree Fahrenheit.

Wow... the site I supplied based upon Hans-discus recommendations were spot on of my appraisal with tank mates!.. Even a blind pig finds an acorn once in a while! 
http://diskuszucht-stendker.de/plugins_en/pdfs/5._Beifische_zum_Diskusaquarium_en.pdf

My original post about tank-mates was solely based upon my last 4 years experience with rearing these guys.. plus the 3 years I had back in the mid-70's (yea.. I'm an old coot)... It's just nice seeing my observations are shared/supported by others that are far more credible in the industry of keeping these fish... 
Bill

Neo....when did you breed Discus??? I had no idea you were doing that now as well as the Angels. Would LOVE to see pics of your breeders and spawns!!    I love Discus but they are just too much work for my taste!