Eh some plants or drift wood but some tall plants are the best bet if you get two angle fish tho make sure they are both females or you could expect bullying or fights
It is almost impossible to buy sexed angels and wouldn't recommend it either. Angelfish are cichlids and females are equally as aggressive as males. I've kept angels since the 80's and currently house 12 adults in a 220g 100% planted tank. In a 100g tank if you want angels I suggest getting 6 small dime to nickel body sized juvies and letting them mature together. Some may pair and some not BUT when angels are kept in a group of 6 or more aggression is minimized and spread out so no one angel gets picked on solely.
Angels also love plants but you have to have lighting that will support plant growth. Angels in a tank that size love Amazon Swords.
If you went with angels you could do:
6 angels
15 cardinal, rummynose, or harlequin rasbora's
15 lemon, diamond, kerri, or emperor tetras
10 cory cats
1 bristlnose plecos (I love longfin albinos, plus albino's tend to stay out during the day which most pleco's don't.
2-3 Whiptail catfish (add only after the tank is about 4-6 months old.
*possibly a smaller school of say 8 threadfin rainbows or marbled hatchetfish for top level swimmers.
You could also do an amazing rainbowfish tank. Rainbowfish come in amazing colors. Check out Oddballfish.com to see many that are available.
Or you could do an African cichlid tank. You have a ton of options.