I find that my goldfish don't eat anything with thick, broad leaves. Anubias are my favourite. I also have some egeria densa. The goldies snack on that a bit, but the stuff grows pretty fast so it can keep up.
I have also heard that java moss and fern are good (I'll be getting some soon), as well as moss balls. I am sure you could probably get away with crypts and amazon swords, too.
HTH!