If you go with more personalized, home-crafted items, you may wish to still use the traditional materials but customize the gift (or have it customized if you don’t feel all that artsy):

• 20th Twentieth year: china – get the signatures of the guest book (signatures of all the guests at the wedding who are now at the anniversary party) by handing them a glass marker (pen that marks on anything and doesn’t erase—like a Sharpie®) and having them sign the china platter you bought.

• 25th Twenty-fifth year: silver – use silver embroidery thread to embellish one of their favorite materials/clothing items/bedding items.
• 30th Thirtieth year: pearl – you could buy an Egyptian-made mother of pearl backgammon board, or you could buy the pearl (opalescent paint and cover the pawns of a chess game with it.  Neatly, of course.
• 35th Thirty-fifth year: coral – How about buying a painting of coral reefs (or of anything, really) and gluing to it some lovely coral from the pet fish store or arts and crafts store—making a beautiful 3-D piece?

• 50th Fiftieth year: gold - There are gold yarns and threads—great for matching gold sweaters, mittens, or throws.  What else could you use gold yarn in?  How about gold flakes?  What could you put the flakes in?  On?

You get the idea.  Now have fun coming up with more of your own!