[Post updated 3/17/08]
When you're looking to make an allergy-friendly sandwich, you can either go it dry without any type of spread, use mustard or ... use a dairy-free, egg-free mayonnaise. Yes, that's right, there are dairy-free, egg-free mayonnaise products out there. I didn't realize this until well into my first year of living with food allergies. Granted, if you've had "regular" mayonnaise, this kind of mayonnaise may not totally compare in terms of creaminess, but for the most part, they do an admirable job in place of the real thing. Here are three products I've tried:
Trader Joe's Reduced Fat Mayonnaise - Good for sandwiches, but would not recommend for something like macaroni salad as it's slightly on the thinner side. Least expensive of the bunch. (Note: This is "made on equipment shared with egg". I've not had a problem with this, but it's important to note for those wanting to play it totally safe.)
Vegenaise by Follow Your Heart - I had to go try this after a recommendation from a reader. I'm glad I did. This is probably the best one I've tried so far with good flavor and creaminess. It will probably hold up well in non-sandwich applications too.
Wildwood's Zesty Garlic Aioli - This is not super zesty. A good option if you want to vary up the flavor a bit.