There are plenty of tetras you could put in with angels. Afterall, many of them come from the same environment as angels. You just need to be mindful of compatability (i.e., neons would be snacks, some tetras are nippy, too large, too aggressive.....) 'Tetras' is a widely encompassing group.
So long as the tetras are too tall to easily fit into an angel's mouth, you can consider them. One tetra I think is underrated are lemons -- a school of those is really pretty. Rummynoses are very cool as well, especially in a planted tank.
Other fish you can consider with angels in a 55 -- swordtails, cories, hatchetfish.......