what besides olive do you put in a martini?
Best is a big garlic stuffed olive. With cheap gin only I also use a pepperoncini now and then. But you gotta try it with a sundried tomato (half if it's big). Anything else?
Well it depends on the martini. A lemon peel "twist" is always nice with gin as are caperberries.
Now, if we're talking vodka, then pretty much anything goes; especially if you get into the flavored arena!
Pickled onions, preferably the large sweet English type. Of course then it isn't a martini anymore but a Gibson.
I also use Pepperdews for a sweet and mild heat thing, blows away pepperoncini. (Stuffing pepperdews with blue cheese makes an amazing cocktail snack!)
I second the caperberries and the lemon twist. For a change a orange twist or grapefruit can be very interesting.
The classic Hendrick's martini is garnished with cucumber slice. I slice a small seedless variety (like israel kirbies) and float in three slices.