A free and easy hand-knitted poncho pattern is the Easy Peasy Knit Poncho from AllFreeKnitting.com. It involves only knit and purl stitches. The pattern works with either light worsted or worsted-weight yarn and needle sizes of 4.5 to 5.5mm.
The pattern uses 120 cast-on stitches. Purl five, and then knit five stitches, repeating until the end of the row. Continue this pattern until the work measures at least 56 inches in length, or more for a longer poncho. At the end, loosely cast off the stitches and block the work to about 28 inches wide. Use mattress stitch to join the short sides, fasten off, and weave in any loose ends to complete the poncho.