I don't even go for BLTs in the first place...if I want a fresh tasting sandwich its vinegar and oil, lettuce, peppers, tomatoes, pickles, olives, and some sort of cured salami of sorts, and I'm good!
However my wife has a penchant for BLTs and has recently changed to preferring ranch dressing instead of mayonnaise. But if you really like mayonnaise (you strange, strange people, you) I can see keeping it simple...BLTs are extremely simple and the more flavor you add the more it obscures the basic ingredients.