Issa sapphire engagement dress

When William and Kate announced their engagement, Kate chose to wear a color that has now become iconic for her, a sapphire or royal blue wrap dress by Issa.

I generally like the dress on her since I think blue is absolutely her color here and she knows it.  It made her skin look so creamy (ah, before all the tanning she does now) and of course the purpose was to highlight the sapphire rock on her finger.  I was actually surprised that the dress is so low-cut, but quite honestly she is small on top so she can get away with it since there's no scandalous cleavage.  (Yay if you have small ones!)

She is so long waisted though and the problem with long waists is finding things that hit you on the waist proper and this dress is just a smidge high waisted on her.  I do absolutely love the way the waist is wrapped though with the wide criss-crossing angled bands.  It really looks great and I just wish the skirt was a bit fuller to balance out the long looking torso, which slimmed the hips a bit.

An expired listing for the dress describes it as a blue silk jersey wrap dress with waist tie and long sleeves.  A true wrap dress is rather open like a robe, but this is just wrap style dress since it has a hidden side zipper.  The waist tie in the dress below is more intricately wrapped along the front of the waist than what Kate opted for, and while I don't think we ever saw the back of Kate's dress, the sash below is tied in the back.

Originally retailed for ≈ $535 U.S. and was as low as $321.

Net-a-Porter - Issa blue silk jersey wrap dress.

This repli-Kate is fairly simple to look for: longer sleeved wrap or faux-wrap style dress in blue.  What we wantis preferably a deep blue but we'll be flexible with the shade since photographs and styling can differ.  Just be sure you find a shade that suits you, be it anywhere between navy or cerulean.
Also it should be noted that in the pictures Kate has her sleeves pushed up slightly to a bracelet length to better show off the ring on her hand, so sleeve length is also flexible.

Our first look-a-likes are actually re-issues by Issa themselves, who re-issued the dress shortly after the engagement announcement only to have the style repeatedly sell out.
As of posting Issa has a version of the dress available at BHLDN.  They don't have any good front side pictures but I figure its as close to the original as you can get since its from Issa themselves.
Retails for ≈ $450

Issa via BHLDN - Lazuline dress.

Issa also has 2 versions of a gathered wrap style dress available on ShopBop.
The one on the left is the actual Kate version but unfortunately is only available in red and "bordeaux" shown below.
The version on the right is more removed from Kate's in that it is a gathered waist style with a considerably lower v-neckline and lacks a waist sash. It is available in a lighter turquoise-y blue shade and the deeper blue shown below.
These dresses retail for ≈ $575 U.S. (left) and ≈ $475 (right).

Issa via ShopBop - long sleeve wrap dress (left) and long sleeve v-neck dress (right).

The Hoss Intropia dress from European retailer John Lewis is a great repli-kate with a similar faux wrapped bodice style.  The v-neckline is softer and looks a little higher but it has a very similar front gathered skirt.

This style retails for ≈ ₤175 or ≈ $276 U.S.

John Lewis - Hoss Intropia jersey dress in blue.

This Macy's version has a criss-cross wrapped bodice, v-neck, and 3/4 length sleeves but but has a smooth slim skirt, not gathered.
Retails for ≈ $64.00 U.S., as low as  $39.99

ElementzB via Macy's - slim three quarter sleeve dress.

This Ann Taylor dress is a truer wrap style so it definitely requires more care in wearing.  The neckline is a surplice wrap and it has a waist sash, but none of the gathered waist or skirt details of the original.
This piece retails for ≈ $128 U.S.

Ann Taylor - 3/4 sleeve jersey wrap dress.