I've noticed that most of the fancy advanced cross stitch designs aren't just floating there in mid-fabric. And, like, duh. Why would you take all of that time with an intricate design and then not bother to finish it off with some flourish? Especially if it's gonna be framed or go on a pillow or something. I've found some nice and interesting patterns for polishing a piece with edgework.
This page has about twenty different repeating-pattern-type boarders of varying complexities.
And there's this awesome little border that accompanied a birdhouse alphabet:
Who knows; depending on what you're working on it could be simply charming.
I found these pretty ones on a website with the coolest name ever: DragonBear.
Of course you can always do something simple, like interlocking hearts or the ever-classic checkerboard. To each piece its own fancy-pants-ness.
And onward we stitch.