Some of my favorite fish that I have either kept or would like to keep:
Corydoras of any species, dumb/kind, whiskery lovable water cows. Will want a sandy area if youre one of those aquascaping guys, I have all sand bottom for mine.
Loaches, for your size tank maybe rosy loaches, these are lively and inquisitive and can be bred.
Kuhlii loaches are also awesome, they like to drape themselves around the plants. Goofy and happiest in groups.
Ottos you will probably get anyway since they seem to be an aquascaper staple, but they are sweet fish in their own right as well.
My favorite "normal" fish is Boraras brigittae, small, red, they have interesting behaviours where a male will pick a small area that he will defend from other males and try to impress the ladies from. Can be kept with shrimp, very small mouths and good natured.
Dwarf shrimp are also really cool and go well with cories and ottos. Not so sure with rosy loaches.
You could go for a pair of small cichlids, they are very intelligent fish and will look right back at you when you look at them. Great parents and lots of personality. Excludes corydoras and shrimp.
Psedomugil species, colorful and lively small rainbowfish.
Stiphodon gobies are a cool addition to a well oxygenated tank. Not good for open top tanks id say.
Epiplatys annulatus, clown killies, have not kept these but nice looking and do well in a small tank.
Dario dario, maybe not for a beginner but small and interesting soft water fish.
Iriatherina werneri, threadfin rainbows. Natural beauty.
Cant think of any others atm, hope this is somewhat helpful, I think you will need to experiment a bit maybe and find the kind of fish you like the most.