Well, of course, it's likely to vary between sexes. People have already mentioned most of the 'generically attractive' goblin traits, though I think I'd add clear skin, as that usually indicates a healthy diet, which you kinda want, as well as red (or whatever the colour of goblin blood is) cheeks, or wherever else they have thin skin, as that tends to indicate health and possibly also the high metabolism so desired by goblins. Alternatively, they might prefer no signs of blood at all, which would indicate unusually thick skin, a possible advantage for them.

The chances are that, for females, what is going to be attractive (on average; obviously, in an intelligent species, there's going to be a wide range of tastes) is things that appear to indicate youth. This is because, regardless of species, the longer you've been alive, the longer your eggs have been bombarded with radiation, which, obviously, causes various defects. This can be seen in humans; the most attractive female voice is, according to this study, a high, breathy tone, typically found in young women. I also theorise that large, firm mammaries are attractive to humans for similar reasons; a large-breasted woman in her forties will look quite different from a large-breasted eighteen-year-old, most of the time at least. Yes, I know that last bit made me sound like some sort of lizard infiltrator. But I have papers to prove I am human. Signed by reputable authorities and everything! I'm not quite sure how this would translate with goblins, but attractive females might well have high, breathy voices by goblin standards, and it's possible they'd have something else which changed with age.

Males, however, cook up new batches of sperm every week or so (can't quite remember, but at any rate it's fairly rapid), and thus don't experience greater incidence of genetic defects as they get older. Therefore, what's attractive is signs of strength and health right now. However, at the same time it's not in the group's interest if one male fathers all the children for three generations, even if he could, for the simple reason that you'll then get inbreeding and that's generally bad. Therefore, signs of male ageing, even when the male in question is still hard enough to knock the teeth down the throat of any challengers, will be unattractive. Note how male-pattern baldness is generally considered unattractive; men with very high testosterone levels (which would normally imply they're fathering lots of children) will often lose their hair at a very young age, which might be an evolutionary mechanism to prevent inbreeding. With goblins, therefore, you'd want a nice, strong man who didn't show signs of testosterone-related aging, whatever those might be. Perhaps something on their skin?

What we've got to take into account, though, is socioeconomic factors. As people have mentioned, having bling on usually means you're doing well. Since goblins don't seem to go for building all that much, most of their wealth would probably be carried on their person, which would save a lot of time working out whether your potential beau can support you in the style to which you have become accustomed (furious, screaming and on fire). As scavengers, they'd likely prefer their mates to have some meat on them, but this could vary between tribes; one that has to move around a huge amount, due to surviving off the sickly members of a migratory herd animal would likely want slimmer, more toned mates than a tribe which primarily lives off berries and other things found immediately around the cave. Of course, it's up to you to decide what exactly their lifestyle is, and thus what body you want.

Also: for monsters which stay in one place, your house could well affect your chances; kobolds would probably prefer someone who can take them on a romantic walk where he shows off all his traps, for instance.

Hope some of that helps!