What size tank? How many swords/platies/other fish do you already have? This is important because if you want schooling fish they need to be in a group of 6 so your tank has to have enough room for them when fully grown. If the tank is 20 gallons or more, I reccomend zebra danios. If smaller, I like black phantom tetras, harlequin rasboras and golden dwarf barbs.
Also, how long has the tank been set up and is it planted (or fake plants)? This can be an issue with some fish - particularly those that require a mature tank or those that are shy.
Cories - especialy pygmy/dwarf cories, would be nice. They are not bottom dwellers though, spending most time schooling in the middle. Other great cories include blackfin, bronze and peppered cories. All of which I have found to be very hardy.