Most guys automatically think lingerie, but my wife doesn't really like negligees, so don't assume yours does. The same is true for church dresses. I'll surprise her sometimes with a dress. I have to accept the fact that she may not like something that I bought and she may not wear it more than once - if at all, but the payoff is worth the risks because when someone compliments her on a dress, she's quick to point out that I bought it for her. Silk pajamas with a matching silk robe are another great gift.
Many ladies find that scented candles on candle stands are romantic.
There are many cleverly designed candle stands from which you can choose and candles come in a plethora of scents. If you're not sure which scent she likes, I recommend vanilla. Avoid being boring. My wife likes a little adventure, but not something exotic like sailing around the world or hiking the Appalachian Trail. Some of these events I've surprised her with.