There are so many options here, depending on what takes your fancy and partly on what your water is like. Tetras and rasboras tend to prefer soft acid water, and most commonly sold livebearers prefer hard alkaline. Though many captive-bred fish are quite adaptable. Danios, bristlenose plecs, most commonly sold corydoras and many gouramis are fine with either.
You could have a feature fish, like an Indian or thick-lipped gourami, and a school of either rasboras or tetras and a group of corydoras for the bottom.
Or if you like an active tank, a school of danios or glowlight danios, a trio of swordtails or platys (1 male, 2 females) and a bristlenose plec.
