If you are set on getting real plants, aquaticusplants.com sells the three most readily available sea grasses I've found: Thalassia testudinum (Turtle grass), Syringodium filiforme (Manatee grass), and Halodule wrightii (Shoal grass). As others have alluded, however, these may not look particularly pleasant to most people, and their care requirements/size can make them less-desirable as well. Also, I have never ordered from the above site, so I can't vouch for if it's good or not (order at your own risk). I do know there are a few other sites that sell one or two of the above, but they can be pretty difficult to find (and, again, I can't vouch for how good they are).
As a note, there are other sea grasses that might be better suited to the average aquarium, but they are not readily available (so if you can find them, they would likely cost a pretty penny comparatively).
As a note, there are other sea grasses that might be better suited to the average aquarium, but they are not readily available (so if you can find them, they would likely cost a pretty penny comparatively).
