The Prince of Wales' website has a downloadable official program and route map. This is really an amazing resource. It includes full file portraits of the couple and an explanation of each of their coat of arms, as well as historical information about Wesminster Abbey.
Sparklebox has pictures of the famous spots along the wedding route to download.
Take a commercial break and check out National Geographic Kids' United Kingdom page.
Activity Village has a wonderful page for kids, including Kate and William royal wedding paper dolls, royal frame handwriting pages, and coloring pages.
Instant Display also has a very nice kids page with educational resources, including bookmarks, coloring pages, vocabulary cards, and Royal Wedding newspaper templates.
The Woodland Trust's Nature Detective's site has this free Royal wedding party kit, woodland picnic style.
Disney's Family Fun has gotten in on the party with a "Happily Ever After" royal wedding page. Don't miss the Princess Kate paper doll with Disney princess and wedding dresses.
Isn't this HappyLand Royal Wedding Set adorable? I think if I'd have found it a little sooner I might not have been able to help myself.
Design Editor has a great set Royal Wedding party printables including a banner and cup wraps.