this one is fairly easy, but you do knit the sleeves in the round, but you don’t have any sewing.
This one is knitted in sections and seamed together:
This one looks pretty easy, and has sewing only for the underarm and side seam:
my favourites: http://www.knittingonthenet.com/patterns/babysweragcard.htm
this one is addictive http://www.ravelry.com/patterns/library/all-in-one-baby-top