McCall's 5845, with inspiration from a Nanette Lepore dress (blogged here). The pattern is out of print, but I found a copy on eBay for a couple bucks.
It's a fab pattern, totally fun and easy to sew. I took my chances and didn't make a muslin since I've had good luck with McCall's sheath dresses before. I made a 14, tapering down to a 16 in the hips and it fits wonderfully. I did add about 3 inches of length to the hem as well.
slip tutorial. Seriously, I think I made this thing in 15 minutes. I simplified it even further by only having one seam up the back. I used a French seam, which is a nice touch.
Thanks to the readers who suggested this pattern to me!