rainbows aren't outwardly agressive but big rainbows do eat small fish and big boesemani can be bullies.
I wouldn't bother about danios but there are numerous tetras that are nice. Black or red phantom, rosy, neons or cardinals, splashing tetras, hockeystick or black neon, Glo-light & diamond tetras are all quite nice.
Neon tetra disease is quite uncommon, however all tetras are prone to bacterial infections that can wipe out the entire tank very quickly. If you quarantine any new fishes for a couple of weeks then you will prevent these types of infections getting into your main display tank. Also avoid buying fish that have just come in. Only buy fish that have been at the LFS for at least a week. If you can, go and check on the fish each day during that time and see if any die. If any of them do die then don't buy them until they get more in, or they haven't had any losses for at least a week. Also look to see if any of the fishes in the tank are pale or have white mouths, these are indications of potential diseases.
If you check out the fish first and don't buy anything from a tank that has had a dead fish in it during the last week, then you shouldn't have any real problems with diseases like bacterial infections.
Cherry, checkered & ruby barbs are nice and peaceful. There are also a few types of small African barb like the 5 or 6 lined barbs. these can be hard to find but usually do well. There are different rasboras like emerald eye, redline & fire rasboras that are nice.
You could get some Melanotaenia praecox (neon dwarf rainbow) they should be fine with tetras. Other rainbowfish include M. papuae, maccullochi, sexlineata & exquisita. There are also blue-eye rainbows like Pseudomugil furcatus, gertrudae, & signifer and Rhadinocentrus ornatus if you can find them.
http
/members.optushome.com.au/chelmon/Melano.htm
There are different Betta species like Betta imbellis & coccinea or sparkling, licorice, honey dwarf & indian banded gouramis.