Ev mentions that he noticed the McDonald's McVeggie burger that he saw when he was here in NYC. Mentioned because they've been "testing" it for years here. I'm suspecting it'll never catch on anywhere else.
A more interesting fast-food test that I've only seen here in Manhattan is over at Wendy's, where they're testing something called Dave's VIP Deal. It's a point-of-sale program for increasing incremental sales by offering to round your purchase up to the next dollar. In exchange for paying those additional cents to add up to a dollar, they give you something small off the menu.
I've only tried it once or twice, and once the total was $6.84. So I paid the additonal 16 cents and I got some (truly nasty) cheese sauce for my french fries. Interesting idea. The better deal was when I had to pay somewhere around 75 cents to round up my order, but I got a side salad in exchange. Saved almost half the cost of the salad. A little bit of planning, and it could actually be almost profitable.
Now none of this is a comment on the quality of fast food; It's uniformly horrible and I know it. But if this kind of pricing program ever goes national, expect a website to pop up promptly that lists what menu items you can get for your change. Of course, I'm probably the only one who's geeky enough to go out for lunch and come back dreaming of a database application...
Addendum: A $4.30 purchase will give you the option to buy an order of fries (normally 99 cents) if you round up to $5.00.