I just finished up a couple of these flannel baby swaddle blankets to give to some soon-to-be babies. Ridiculously easy and hopefully useful!
I used the pattern by Prudent Baby's Jaime Morrison Curtis that I found in the book Fabric-by-Fabric One Yard Wonders (given to me by the always-thoughtful Colleen). However, it looks like there is also a tutorial for the blanket on Prudent Baby if you don't have access to the book.
Pretty easy: three pattern pieces, one yard of flannel, three packs of bias tape... it's basically a giant triangle blanket with two built-in ties sewn onto the back to keep the swaddle secure. My wrinkly, babyless photos don't really do it justice (and Lincoln was not feeling like modeling this morning), but you can see it in action here.