Pretty much all of them. Hornwort or a similar plant that floats in a big tangle is particularly good, pencils like to dart in and out of cover. If it's hockey stick pencils (the diagonal ones) that you're talking about, you'll definitely want a thicker cover, so maybe something like red root floater or water lettuce, depending on legality and space.
I have Golden Pencilfish, Nannostomus Beckfordi, and mine really enjoy Frogbit. They sleep under it and eat the hair off the roots during the day. The Frogbit shoots out roots like crazy so it doesn't seem to be harming the plants. Win win.
I have dip tails with frog bite. I have had them now for going on two years they really like to hanging out under floating plants. But there a lot different than beckfordi. If your going to keep the beckfordi you won't need floating plants there more of a mid water swimmer. It's not they won't appreciate the cover they just don't get to the top much. The dip tail are up at the top all the time think hatch fish. They make up for there lack of color by there behavior.