For my WordPress site, I added a new text widget to my sidebar.
The HTML is straightforward. The URL input parameters for DDG can be found here. What I really like is that DDG provides URL parameters to control both the font and highlighting colors of the search results.
By using the form input type of "search" I get a nice looking search box on Webkit browsers like Safari and Chrome.
On Firefox and IE, the search box looks a little less attractive but functions the same. Type a search and hit the return key to get a nicely formatted DuckDuckGo result set.
The only thing I think the DDG search is missing, is accurate date sorting. Even though there is a sort-by-date flag, it doesn't work well for me. I still prefer it to Google and I like that the searching does not take up cycles on my host. It's all handled by DDG.