Two things will tell you what the perfect anniversary gift would be: Your wallet and your wife.
Even the most romantic of spouses doesn't want to wind up with the family credit cards being frozen because you went overboard with your gift, so price is always a crucial factor. It is not, however, the only one. Let's say that your neighbor's wife was thrilled with her anniversary present - a trip to Hawaii. If you buy the same for your sun and sand hating wife, you are not only telling her that you put no effort into getting her a gift but you don't even bother to pay attention to what she tells you.
Listen when she tells you about the things that she wants, likes, or feels that she needs. Tailor your gift to meet her desires. It might be anything from a visit to a beauty spa to her own a simple candle-lit dinner on your own back porch. Just keep in mind that there is no such thing as the perfect "one gift fits all" present. Years ago, a well-known perfume advertisement advised, "Promise her anything, but give her Arpege." The ad executive who approved that one undoubtedly had a great career - and is currently working on his fourth marriage.
Those two factors - the price and her tastes - are the crucial ones in choosing an anniversary gift for her. A third one, a touch of romance, can be the icing on the cake. Provide that by giving her proof that your memory of that all-important day when you married is as meaningful to you as it is to her. Think back to your wedding day and your honeymoon choose a gift which has some connection to something that happened. If, for example, the band at the reception played a melody of Abba songs, you might want to take her to see "Mami Mia". Don't worry - she is almost certain to remember a reference like that and, if she doesn't, you will score extra points as you remind her of it.