How many angelfish do you have in there? You shouldn't be keeping more than three in a 30 gallon or they're overcrowded. Just a tip for you. =)
To help you pick a plant, you should tell us what the tank is like. What lights do you have, what fertilizers are you using, if any, do you have CO2 on it, what is your substrate (bottom-sand/gravel/etc)...are you thinking of something fast growing and easy to take care of, or something more challenging? Do you want something green or something with some color to it...red, maybe? Tall or short? What plants do you already have? There's hundreds of options you could choose from lol.
Since I don't know how experienced you are, here's some nice beginner plants that do well in most conditions: green hygro, sunset hygro, amazon sword, anacharis, ludwigia repens (red ludwigia), cryptocoryne species, and anubias species.
only have four angelfishs t-5 twin light, so far swordplants, using co2 exal, using sand gavel/clay latare mix, been with plant for while now, it just that it hard to find the right plants since it tall. mis of some green and red plant would be nice
All stem plants will be as tall as they can be, when they get good CO2, which you absolutely must have with that lighting, and good fertilizing. Just don't try Amazon Sword plants or any other similar sword plant. Those would very soon completely fill that tank.
Most Vals will grow more than tall enough for any tank too. They can easily grow 3 feet tall.
It sounds like stem plants or vals would work well for you...they will grow as tall as the tank and then some. Look through the swap n shop board here, you could get some good deals on stem plants or whatever else.
Yes, the swordplants do tend to take up a lot of room...I threw away four of them out of a 55 gallon tank because they filled it completely up and blocked out all the light from my stem plants.