This is as basic as you can get. I wrote out this pattern for someone who wanted a turtle neck poncho. You can also make it with a crew neck or just 4 to 6 rows (2 to 3 ridges) of garter stitch.
The sample was knit without changing to smaller needles for the garter stitch edge and that is what gives it a slightly ruffled look. If you go down 2 needles sizes for the edging, it will lie flat. Seed stitch edging also looks great, but again I recommend using the smaller needles for it.
Seachange check out the Patons and Cleckheaton sites for free patterns too. If you join the kniterati (on either site) they should send you a free current pattern (you choose, easy, intermediate or hard). I don't know if they have ponchos available but worth looking through the patterns.