Aquatic plants in a goldfish aquarium? Sure, you say, my goldfish will love me for providing them with an expensive salad bar! Not necessarily. Although it is true that goldfish will happily munch down the majority of aquatic plants, there are some that are so tough, spiky, or generally inedible that they can survive your goldfish's appetite for veggies. And, yes, stay around long enough look beautiful in that goldfish aquarium of yours!
Give some of these live plants a try in your goldfish aquarium. Not only is it nice to finally toss the plastic plants (in my opinion the lush green of these live plants is much more beautiful), but the plants will thrive on the excess of nutrients that your goldfish are producing-- and your goldfish will appreciate that as well!
Java Fern - The leaves of Java fern (Microsorum pteropus) are much too tough for goldfish to eat. I've had Java ferns in my goldfish tank for years. Luckily Java ferns come in a number of different varieties now, so you do have a selection. My favorites are the Tropica and the Windelov varieties. The Tropica has what may best be described as a multi-fingered hand appearance, and the Windelov variety is slightly shorter, with a fringed look at the top. I also still like the original variety. All varieties will do well in the cooler water usually found in goldfish tanks, and they actually do nicely under low light. In addition, the roots of Java ferns shouldn't be buried in gravel, and can instead be tied (with thread, or rubber bands) to driftwood and rocks. If you are keeping a bare-bottomed goldfish tank, then this plants-on-driftwood thing can be ideal.
Bolbitis heudelotii - This plant is also too tough for the goldfish to graze upon. Much like Java fern, Bolbitis does well in cool water, doesn't require high light, and can also be tied to driftwood and rocks. This is a beautiful plant and I would recommend it even for tanks without goldfish.
Hornwort (Ceratophyllym demersum) - The needles of this plant are usually too spiky for the goldfish to eat. I say "usually" because this plant will survive in the goldfish tank for a good long while- until you go on vacation for a few days, and then your goldfish may decide he is hungry enough to eat those hornwort needles anyways! Chances are, though, enough will survive that carnage to quickly start producing more, as soon as your goldfish starts getting his normal feedings again. If you want to try it- Hornwort really likes the cool water of goldfish tanks, can be "rooted" (it actually modifies its buried leaves to act like roots) or left to float around the aquarium, and prefers medium to high lighting.
Frogbit (Limnobium laevigatum) - also called "floating hearts". These large floating plants look beautiful on the water's surface. They are generally too large to be eaten, although the goldfish may nibble on the long roots a bit. These plants prefer high light.
Anubias barteri - I have to admit that I have not tried including plants of the Anubias species in a goldfish tank, however I suspect that these tough-leaved plants (especially the nana and barteri varieties) would do quite well. These plants in general do well under low light, although they may prefer slightly warmer water. If you have had success with these in a goldfish tank I would love to hear about it.
Pothos and Philodendron - These are not aquatic plants, they are actually popular vine-like houseplants. However these plants do very well with their roots in just water (this is also how new cuttings of these plants are usually started) and are terrific at sucking out the ammonia and nitrates from the aquarium water. They also look nice draped all around the outside of your fish tank!
Duckweed (Lemna minor) and Salvinia - Yes, yes, it is quite true that these will be eagerly gobbled up by your goldfish! However if you do have these quickly-reproducing plants taking over the surface of your other fish tanks, throwing in handfuls of duckweed and salvinia will keep your goldfish very happy (and slightly help you keep things under control in your other tank!)
I hope these suggestions help with your goldfish tank aquascaping. Although the selections are a bit limited, gorgeous tanks can be designed with just these plants and maybe a few rocks and driftwood pieces. Also, feel free to experiment with other plants... at the worst, your goldfish will thank you for the salad bar if the experiment "fails!"