Tuesday, January 22, 2013 at 11:36 AM 
The first lady wears a custom ivory wool-applique 3/4 sleeve coat and dress by Naeem Khan for the National Prayer Service this morning at the Washington National Cathedral. Note the jeweled neckline and trim. J.Crew Valentina patent pumps in Apricot Mist complete the neutral mix. So chic!
J.Crew, Naeem Khan Saturday, April 28, 2012 at 10:12 PM 
The President and First Lady are attending the White House Correspondents' Dinner this evening. For the occasion, Mrs. O has chosen a strapless printed gown paired with gold hoop earrings. Gorgeous!
Update: Mrs. O has once again turned to Naeem Khan for a formal event, wearing the designer's strapless paisley print organza ballgown. On the jewelry front, the First Lady wears the "Aurora" earrings by designer Carla Amorim, featuring 18k rose gold with cronaline and orange sapphires, as well as a ring by Sara Weinstock (not seen above, but visible in other photos).
Red Carpet Live Blog [Politico]
Carla Amorim, Naeem Khan, Sara Weinstock Sunday, February 26, 2012 at 8:18 PM 
The President and First Lady are hosting the 2012 Governors’ Dinner in the State Dining Room of the White House this evening. As in recent years, limited press photos have been published. Fingers crossed for a full length view on the White House Flickr feed!
For a three-quarter length image:
"Forget the Oscars" [Daily Mail UK]
Update: The First Lady wears a one-shoulder floral beaded metallic sequin gown by Naeem Khan.
Naeem Khan Tuesday, June 7, 2011 at 6:32 PM 
Photos by Charles Dharapak / AP Images, Jewel Samad / Getty Images
The President and First Lady are hosting German Chancellor Angela Merkel and her husband Joachim Sauer for a State Dinner at the White House this evening.
For the occasion, Mrs. O has chosen a stunning ivory chiffon gown with linear crystal beading by designer Naeem Khan. An armful of Alexis Bittar bangles complete the look.
Naeem Khan has certainly become one of the First Lady's go-to designers for formal events! This is the third Naeem Khan gown that Mrs. O has worn since November 2009.
Alexis Bittar, Naeem Khan Wednesday, May 11, 2011 at 6:55 PM 
Image by Charles Dharapak / AP Photo
The First Lady hosted a poetry workshop for students at the White House today, wearing one stunner of an embellished, embroidered pencil skirt. I believe we may have seen a glimpse of this once before, but not yet had a chance to admire it in its full glory. A stack of bracelets and turquoise earrings complete this fabulous look.
Update: Indeed, as several suggested, the skirt is by Naeem Khan, from the designer's Spring 2009 collection. The tank is also Naeem Khan, in dusty rose cashmere.
"First lady hosts young poets at the White House" [Washington Post]
Naeem Khan