I a 5 gallon, if you are newer to the hobby, I would look at zoas, pompom xenia (you will need to frag/prune it eventually), ricordea, mushrooms, sympodium, Liam's clove polyps, violet cespitularia, and yumas just to name a few.
In such a close fit if you are looking to branch into LPS I would look into duncans, candy canes, or fox coral. Just a word of caution it is very tricky to keep calcium and alk levels right in such a small volume of water! So unless you are set on LPS I might avoid them for a while and get your feet under you. If you had a bigger tank it would be a bit easier to establish and keep those levels consistent. Things change VERY quickly in smaller volume tanks. I loved the challenge of my nanos.