Apple provides an excellent site search design, which includes an AJAX auto-completion drop down menu showing categorized matches against your query, and thumbnail images of matching items. The categories carry over in the search results page, which displays your results in collapsible sets, much as you would see with the Mac OS Spotlight search. Some result sets are even rendered as a carousel (look at iTunes results).

1. Auto-completion drop down shown for query on "iph."
2. Search shown in page context.
3. Search results sets.
4. Doing a search for "virus" displays a nice little easter egg. (Thanks, Mark, for the tip)