Angels and keyholes would work well. Instead of keyholes, you could also do a pair of blue rams or a trio of apistos (borelli are my favorite).
I personally prefer to avoid anything that would compete visually (in size) with these two species. (I've done such a tank in the past). I also like to keep things somewhat biotope faithful. So, with that in mind, this is what I would do:
1. One very large school of rummynose tetra. These are beautiful fish that school well and in a 55 you could do 20. They compliment black veils very nicely and are generally too big for the angels to eat.
2. A school of false julii cories i.e. trilineated. Their coloration will also be a nice compliment to black angels (could do panda, too.) I'd say six
3. A beautiful albino long-finned BN pleco (or two). These seem not to get as large as other BNs and their flowing fins are a lovely compliment to the angels. I adore mine!
That's it. Over time, I've found that the nicest tanks are those that don't have a gazillion different species in them.
Also, this should be planted!
Good luck!