A 20th wedding anniversary is big milestone. Through these many years, you have stood side-by-side with each other through thick and thin, and it should be commemorated in a special way.
If you want ideas for gift for the wife, it can be a fine set of china, or jewelry in platinum (platinum cufflinks for the husband), emerald, or diamond. 
And who to say that you have to limit yourselves to the traditional gifts? If you're giving gifts to each other, the gift should be meaningful. Explore annivesary ideas that are sentimental and romantic. 
How about treating your spouse to an anniversary vacation?