Prom Dress Advice! Watch
I am 5'ft 7, rather well built (size 14), with fair skin/reddish hair!
Thinking so far about a long dress in an earthy shade or blue/green.
If you have little boobs, a halterneck dress or something that shows off your shoulders and back could be really nice, and you could cover up with a wrap if needed. If you have bigger boobs, avoid anything that squishes them [e.g. strapless dresses might not stay up unless they're digging in, and that's not so nice. But you could try them on and see anyway].
Try a variety of cuts... things that are very structured, e.g. with corset-style tops, and things made of more flowing material. You don't have to wear anything right down to the ground - something with an asymmetric hem line from knee length could look stunning and a lot less 'Ooh I'm a princess disguised as a meringue'.
If you've got a well defined waist, you could try dresses that cling around there and then skim down over your hips. Alternatively, you could try something that has a more structured middle and will define your waist more for you.
It's hard to say what would work well without seeing you... can you describe yourself a bit more?
Edit: there are some nice dresses here - they've got a variety of styles and cuts, but they're all quite elegant [sorry, there's other stuff in the slideshow too, but plenty of prom-style dresses]. There are far too many 'Wahey, I've got titties and legs, and a bottom, woohoo, look!' prom dresses on a lot of sites =/
Another edit: This is great! It's too big on her boobs, but other than that, it's really nice. It shows off her back without being slutty, and it's got texture of its own around the waist and hips, which will help to hide any bumpy bits. Another bit of general advice is to draw attention to the body bits you like, and find an outfit that skims over or disguises the bits you don't like so much. I guess that green dress is a bit of a contradiction, because the texture at the waist draws your eye to there, but also has to potential to be very flattering.