I like them chunky rather than creamy, so I mash the yolks roughly instead of processing them. Then I add finely chopped celery, carrot and red pepper. Lots of pepper and salt along with the mayo and mustard. (This makes a great egg salad sandwich, too.)
For a fancier party (wedding lunch maybe?), add a little sour cream to the mayo (no mustard), process the yolks to a puree and top with a bit of red caviar.
I once tried flavoring the yolks with mashed avocado and a put a little salsa on top. It was edible but the color was nauseating.
The eggs will peel easily every time if you poke a hole in one end with a pin before cooking. When they're done, plunge them into ice water for 10 minutes before peeling.
I've seen a product that combine mayonnaise with mustard (made by French?). Seems like a marketing gimmick to me, but might be handy if you need to make hundreds of devilled eggs.
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