We have been taught that 'gustar' is an unusual verb and that you only ever use 'gusta' or 'gustan' depending on whether you like singular or plural things.
Would you use 'me gustas' to say 'I like you'?
Yes, me gustas is correct way to say this.
Gustar is "unusual" in the way that it doesn't mean "to like", but rather "to be liked by". "to please"
It's absolutely not true that you only ever use gusta or gustan.
Consider few examples for each grammatical person:
Ya no te gusto — You don't like me anymore
Me gustas — I like you
Me gusta España — I like Spain
Sé que os gustamos — I know that you like us
No me gustáis — I don't like you (plural)
No me gustan los toros — I don't like bullfighting
A remark regarding usage. I'm not very sure what you mean exactly by
I like you in English (from a person to another). But in Spanish, if you say
me gustas, this is in a more-than-friends sense. In a just-as-friends context, it's better to use
me caes bien or
me agradas. I think
me gustas is more like
I have a little crush on you. Be careful with that.
As @vartec said,
me gustas is correct. A great way to think about gustar in English is to imagine a word gust that means the opposite of disgust. Just like you would say
that person disgusts me, with this imaginary word gust, you would say
that person gusts me, meaning he or she pleases you, the opposite of disgust.
Or, for the case is question,
you gust me, which would then translate back to
Read more at thelearninglight.com.
The other answers have focused on using gustar in the structure that it's normally taught in Spanish classes where *gustar takes an indirect object pronoun. While the most common use is absolutely either gusta or gustan (see this Google N-Gram, I omitted valid forms that weren't found so I could fit it all in a single search), the other forms, as you can see, are certainly used.
There is also another way to use gustar that mirrors the English construction a bit more closely (and is identical to modern Portuguese), although it will come off very formal in modern Spanish. See the comparison:
To use this structure, you use gustar with the same subject you would in the English statement, and follow it with the preposition de. The thing that is liked is the object of that preposition.
Finally, gustar can be used to mean like/wish/want/prefer and in this case it is actually a transitive verb, as in ¿Gusta Vd. un vino tinto? (would you like a red wine?) or Haz como gustes (do as you will/wish). This usage is very rare outside of, well, basically the two phrases (with minimal variation for subject/object) I gave ;-)
No, it is not correct. At least not grammatically correct. While it may be accepted in casual conversation, gustar is conjugated with either a singular or a plural ending. The person is not doing the action, rather represents a single noun that has an effect on a person. ie. Juan a mí me gusta. or Tû a mí me gusta. In this case, the subject pronoun 'you' is not doing the action, therefore the second person tense is not employed. Rather, another item, a singular noun, which happens to be a person, is having an effect on a person. It's comparable to saying that person makes me .... If you require more explanation, look in 501 verbs. It's a great resource. Thanks. Buena suerte.