Estás en linea

This is another situation where literal translations just don't work.

When you tell someone...

Estás en linea

You're telling them they look trim, perhaps athletic and has a nice body in general.  In more generic terms you'd say "estás en buena forma".

And there's the expression...

Estás en linea curva

Which means just the opposite.  Now you're talking about someone who's not in "buena forma", but instead gordo or gorda (fat).

Since we're on the topic of giving out compliments, let's continue our discussion about hot bods.  

Cuerpo means "body", so you could say:

Tienes buen cuerpo
You've got a nice body

 But if you're really moved by someone's physique, then you want the word cuerpazo.  A cuerpazo is a really great body.

¡Qué cuerpazo tienes!
You've got a really great body

You can use "bien bueno".

Este chico esta bien bueno
This guy is really hot

And for a woman:

Esta chica esta bien buena
This girl is really hot

Now it's time to get gender specific.  Ladies, here's a few words for you first.

A galán is what we call a hunk.   Most women seem to think Brad Pitt and Denzel Washington are galanes. 

There's also papacito.  This can be used as a term of endearment as well as saying a guy is a total hunk. 

Guys, get ready, it's your turn.

A mamacita is a way of saying a woman is totally hot.  Also a possible term of affection.

Mira esa mamacita
Look at that sexy girl

A buenota is also a very attractive woman.

La novia de Juan es una buenota
Juan's girlfriend is super hot

Well, I think that's more than enough to get you started.  Keep in mind while none of these phrases are explicit, most of them are meant for you to use with friends.  It's like using the word hottie in English, some people will be offended, some won't. 

If you're looking for terms a little less colorful, you can also go with hermoso/a, guapo/a, or bonita.  And it's my understanding that men are never called bonito. 

 If you're not familar with hermosísimo/a and guapísimo/a  they're another way of emphasizing that someone is really beautiful or handsome.   You can also do the same thing with reguapa and rehermosa.  When you add the prefix "re", it intensifies the meaning.  You can tack on "re" to many words in Spanish, like rebueno.  It's not just good, it's really good.

This soup is really good
Esta sopa es rebuena

That's it.  Have fun with these!

¡Hasta la próxima!