Often times I just slip stitch but there are times when I want the edge to look seamless and slip stitch join just doesn't get that. I have come up with this method. This is demonstrated on my craft exchange item (but it's to close to tell what I'm making so HA!). You can click on any image for a larger view.
1st a reminder that I am left handed.
When you finish your last stitch do not do a slip stitch join. Break/cut your yarn and pull the end through your last stitch leaving it unattached to the beginning.
Thread the yarn onto a darning needle. You can use a hook also. Now stitch through the same place where you would do a slip stitch join as shown.
Now bring the yarn down through where your yarn came from on the last stitch through as shown here.
When you pull this tight to match the tension in the project the stitch is now "lost" on the top edge. Looks exactly like the rest of the stitches.
Note: This does add 1 stitch to the edging. If you do not want the added stitch you can pull the yarn to close the gap.
Now I like to run my needle back under the side side of the beginning chain up. This creates the bottom hump that you get when you do a normal chain.
Weave your end n as you would normally do per your preferred method.