>If you're 30+ and have a mildy casual white collar career, brown and black loafers are pretty standard. Pair that with something like chinos and a button down shirt. You can wear invisible socks with those or standard dress socks.
>Dressed up depends. Your loafers can play double duty these days. If you really want to look sharp and are pulling out the suit and tie, try brown or black cap toe oxfords. Wearing a tux? Black patent leather opera pumps or patent leather cap toe oxfords.
>Casual depends on how you like to look in your off time, loafers are again popular with more traditional casual ensembles, but you could wear clean old school white canvas sneakers and look classy with the right outfit.