I really like the potholder I made for NerdWars (on Ravelry) this month. (I used Peaches & Creme and size 7 needles.) Ilana MacDonald's pattern can be found here.
It's my first try at double knitting. It took me quite a few tries to get it looking the way I'd like. And, as a bonus, my gauge got more nearly even with each try. ;)
I probably did the edges "incorrectly". But, at least, they're something I like.
Here are my adventures:
The first thing I tried for the cast on edge was casting both colors on at the same time. But, I didn't like the look and so ended up working a provisional cast on in red and then knitting yellow on one side and red on the other.
For the side edge, I first tried working the edges just as I would any other stitch in the row. The edge looked sloppy. And, I wasn't sure how easy it would be to crochet the edges together when done. Then I tried slipping the first stitch of every row. That was a little better. Then I tried knitting the 2 yarns together at the end of a row and slipping the first stitch at the beginning of a row. That gave an edge that was thicker than the rest of the potholder. I finally ended up slipping the first 2 stitches of every row (1 st in each color) and then twisting the yarn so that the edges would hold together even before the crochet edging was added.
Finally, for the top .... (since I was pretty sure I had broken most of the "rules" for double knitting anyway) .... I repositioned all the sts (2 at a time) and worked a sc in red through each pair (1 of each color).
From there it was easy to single crochet around (working extra sc's in the corners).